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Abstract:

Disclosed is an integrated process for the preparation of
1,4-cyclohexanedimethanol from terephthalic acid. Terephthalic acid is
esterified with (4-methylcyclohexyl)methanol and the terephthalate ester
hydrogenated to 1,4-cyclohexanedimethanol in a 2-stage process. The
(4-methylcyclohexyl)methanol that is formed during the hydrogenation step
is recycled to the esterification reaction. Also disclosed is a method
for purifying and recovering the 1,4-cyclohexanedimethanol product.

Claims:

1. A process for the preparation of a 1,4-cyclohexanedimethanol from
terephthalic acid, comprising: (i). contacting terephthalic acid and
(4-methylcyclohexyl)methanol in a mole ratio of alcohol to acid of at
least 2:1, in a reaction zone at a temperature of about 200.degree. C. to
about 300.degree. C. under superatmospheric pressure, while removing
water from the reaction zone, to form an esterification product mixture
comprising bis(4-methylcyclohexyl)methyl) terephthalate and unreacted
(4-methylcyclohexyl)methanol; (ii). contacting the esterification product
mixture with hydrogen in a first hydrogenation zone in the presence of a
catalyst effective for hydrogenation of an aromatic ring to produce a
liquid effluent comprising bis(4-methylcyclohexyl)methyl)
cyclohexane-1,4-dicarboxylate; (iii). contacting the effluent from the
first hydrogenation zone with hydrogen in the presence of an ester
hydrogenation catalyst in a second hydrogenation zone to produce a
hydrogenation product comprising 1,4-cyclohexane-dimethanol,
4,4'-oxybis(methylene)bis(methylcyclohexane), and
(4-methylcyclohexyl)methanol; (iv). distilling the hydrogenation product
from step (iii) to recover a distillate comprising a majority of the
(4-methylcyclohexyl)methanol in the hydrogenation product and a
distillation bottoms comprising a majority of the
1,4-cyclohexanedimethanol and
4,4'-oxybis(methylene)bis(methyl-cyclohexane) in the hydrogenation
product; (v). allowing the distillation bottoms to form an lower layer
comprising a majority of the 1,4-cyclohexanedimethanol in the
distillation bottoms and a upper layer comprising a majority of the
4,4'-oxybis(methylene)-bis(methylcyclohexane) in the distillation
bottoms; (vi). separating the upper and lower layers of step (v) and
recovering the 1,4-cyclohexanedimethanol from the lower layer by
distillation; and (vii). recycling at least a portion of the
(4-methylcyclohexyl)methanol to step (i).

2. The process according to claim 1, wherein the temperature in step (i)
is about 220.degree. C. to about 280.degree. C. and the pressure is about
1.4 bars gauge to about 6.9 bars gauge.

3. The process according to claim 1, wherein the ratio of alcohol to acid
in step (i) is about 2:1 to about 3:1.

4. The process according to claim 1, wherein the water is removed from
the reaction zone in step (i) by distillation and wherein step (i)
further comprises recovering (4-methylcyclohexyl)methanol from the
esterification product mixture by distillation and recycling to the
reaction zone of step (i).

5. The process according to claim 1, wherein the terephthalic acid and
(4-methyl-cyclohexyl)methanol are contacted in the absence of an
exogenous catalyst.

6. The process according to claim 1, wherein all or a portion of the
(4-methylcyclo-hexyl)methanol is contacted with the terephthalic acid is
recycled from process for the preparation of CHDM by hydrogenation of
bis(4-methylcyclohexyl)methyl)terephthalate.

7. The process according to claim 1, which is a continuous process.

8. The process according to claim 1, wherein the esterification product
mixture comprises at least 70 weight percent of
bis(4-methylcyclohexyl)methyl)terephthalate.

9. The process according to claim 1, which comprises contacting the
terephthalic acid and (4-methylcyclohexyl)methanol in a fixed bed or
stirred reactor.

10. The process according to claim 1, wherein the terephthalic acid is
added incrementally to the reaction zone.

11. The process according to claim 1, wherein the esterification product
mixture in step (ii) is contacted with hydrogen at a temperature of about
150 to about 350.degree. C. and a pressure of about 50 to about 400 bars
gauge and the catalyst effective for hydrogenating an aromatic ring
comprises palladium, platinum, nickel, ruthenium or combinations thereof
deposited on a catalyst support material.

12. The process according to claim 1, wherein the esterification product
mixture in step (ii) is contacted with hydrogen at a temperature of about
180 to about 300.degree. C. and a pressure of about 50 to about 170 bars
gauge, the catalyst effective for hydrogenating an aromatic ring
comprises palladium, ruthenium, or combinations thereof, and the catalyst
support material comprises alumina, silica-alumina, titania, zirconia,
chromium oxides, graphite, silicon carbide, or combinations thereof.

13. The process according to claim 1, wherein the catalyst effective for
hydrogenating an aromatic ring comprises palladium on alumina.

14. The process according to claim 1 wherein the effluent from the first
hydrogenation zone in step (iii) is contacted with hydrogen at a
temperature of 180 to about 300.degree. C. at a pressure of about 40 to
about 400 bars gauge and the ester hydrogenation catalyst comprises at
least one Group VIII metal, a copper-containing catalyst, or a
combination thereof.

16. A process for the preparation of a 1,4-cyclohexanedimethanol from
terephthalic acid, comprising (i). contacting terephthalic acid and
(4-methylcyclohexyl)methanol in a mole ratio of alcohol to acid of about
2:1 to about 5:1, in a reaction zone at a temperature of about
220.degree. C. to about 280.degree. C. in the absence of a exogenous
catalyst under super atmospheric pressure, while distilling water from
the reaction zone, to form an esterification product mixture comprising
bis(4-methylcyclohexyl)methyl)terephthalate and unreacted
(4-methylcyclohexyl)methanol; (ii). recovering unreacted
(4-methylcyclohexyl)methanol from esterification product mixture by
distillation to form a purified esterification product mixture and
recycling the unreacted (4-methylcyclohexyl)methanol to the reaction zone
of step (i); (iii). contacting the purified esterification product
mixture with hydrogen in a first hydrogenation zone in the presence of a
palladium on alumina catalyst to produce a liquid effluent comprising
bis(4-methylcyclohexyl)methyl)cyclohexane-1,4-dicarboxylate; (iv).
contacting the effluent from the first hydrogenation zone with hydrogen
in the presence of a copper chromite catalyst in a second hydrogenation
zone to produce a hydrogenation product comprising
1,4-cyclohexane-dimethanol, 4,4'-oxybis(methylene)bis(methylcyclohexane),
and (4-methylcyclohexyl)methanol; (v). distilling the hydrogenation
product from step (iv) to recover a distillate comprising a majority of
the (4-methylcyclohexyl)methanol in the hydrogenation product and a
distillation bottoms comprising a majority of the
1,4-cyclohexanedimethanol and
4,4'-oxybis(methylene)bis(methyl-cyclohexane) in the hydrogenation
product; (vi). allowing the distillation bottoms to form a lower layer
comprising a majority of the 1,4-cyclohexanedimethanol in the
distillation bottoms and an upper layer comprising a majority of the
4,4'-oxybis(methylene)-bis(methylcyclohexane) in the distillation
bottoms; (vii). separating the upper and lower layers of step (vi) and
recovering the 1,4-cyclohexanedimethanol from the lower layer by
distillation; and (viii) recycling at least a portion of the
(4-methylcyclohexyl)methanol from step (v) to the reaction zone of step
(i).

17. The process according to claim 16, wherein the amount of
(4-methylcyclohexyl)-methanol in the hydrogenation product is sufficient
to satisfy the (4-methylcyclo-hexyl)methanol required for step (i).

18. The process according to claim 16, wherein all or a portion of the
(4-methylcyclo-hexyl)methanol that is contacted with the terephthalic
acid is recycled from a process for the preparation of CHDM by
hydrogenation of bis(4-methyl-cyclohexyl)methyl)terephthalate.

19. The process according to claim 16, which is a continuous process.

20. The process according to claim 16, wherein the upper layer comprises
10 weight percent or less of 1,4-cyclohexanedimethanol, based on the
total weight of the lower layer.

21. The process according to claim 16, wherein the upper layer comprises
5 weight percent or less of 1,4-cyclohexanedimethanol, based on the total
weight of the lower layer.

22. The process according to claim 16, wherein the upper layer comprises
at least 70 weight percent of
4,4'-oxybis(methylene)bis(methylcyclohexane) based on the total weight of
the upper layer.

23. The process according to claim 16, wherein the upper layer comprises
at least 80 weight percent of
4,4'-oxybis(methylene)bis(methylcyclohexane) based on the total weight of
the upper layer.

Description:

FIELD OF THE INVENTION

[0001] This invention pertains to an integrated process for the
preparation of 1,4-cyclohexanedimethanol by esterification of
terephthalic acid and the subsequent catalytic hydrogenation of the
terephthalate diester. More particularly, this invention pertains to a
process for the preparation of 1,4-cyclohexanedimethanol in which the
by-products of the hydrogenation process are recycled as raw materials
for the preparation of the terephthalate diester feedstock and in which
the purification of the 1,4-cyclohexane-dimethanol product is simplified.

BACKGROUND OF THE INVENTION

[0002] Cyclohexanedimethanols are important intermediates for producing a
variety of polyesters for coatings, fibers, molding plastics, packaging
materials, and the like. Cyclohexanedimethanols are typically
manufactured by the hydrogenation of the corresponding
cyclohexanedicarboxylate esters. For example, one of the more
commercially important cyclohexanedimethanols, 1,4-cyclohexanedimethanol
(abbreviated herein as "CHDM"), typically is prepared by a two-step
hydrogenation process involving hydrogenation of dimethyl terephthalate
(abbreviated herein as "DMT"), to give dimethyl
1,4-cyclohexanedicarboxylate (abbreviated herein as "DMCD"), followed by
hydrogenation of the ester groups. The various steps of this process have
been described, for example, in U.S. Pat. Nos. 3,334,149, 6,919,489;
5,399,742; 5,387,752; 5,395,987; 5,185,476; and 7,632,962; and United
Kingdom Patent Application No. 988,316.

[0003] The use of DMT as starting material for the preparation of CHDM
presents several challenges. DMT is typically prepared by the
esterification of terephthalic acid with methanol under high pressures
and temperatures that requires expensive, specialized process equipment
and can result in increased energy consumption and operating costs.
Further, during the esterification process, DMT tends to form solids
within the reflux zones of the process, which can cause plugging and
reduce the efficiency of the heat exchange surfaces. Other solvents such
as, for example, xylene may be introduced in the reflux zone to help
liquify the DMT, but this solution places additional purification
requirements on the DMT process. DMT must also be distilled prior to its
introduction into the hydrogenation step of the CHDM process in order to
remove partial esterification products and any esterification catalysts
that can poison and/or reduce the activity of the downstream
hydrogenation catalysts. Finally, the hydrogenation of DMT releases
methanol that requires additional purification and processing steps in
order to recover and recycle the methanol from the CHDM hydrogenation
product mixtures. The use of alternative CHDM feedstocks that avoid these
difficulties, therefore, could greatly improve the efficiency and reduce
the equipment and processing costs of the CHDM process.

SUMMARY OF THE INVENTION

[0004] It has been discovered that 1,4-cyclohexanedimethanol may be
efficiently prepared in a simplified process that comprises the
preparation of the bis(4-methy-cyclohexyl)methanol diester of
terephthalic acid followed by hydrogenation of this ester to produce the
CHDM. One embodiment of our invention, therefore, is a process for the
preparation of 1,4-cyclohexanedimethanol from terephthalic acid
comprising: [0005] (i). contacting terephthalic acid and
(4-methylcyclohexyl)methanol in a mole ratio of alcohol to acid of at
least 2:1, in a reaction zone at a temperature of about 200° C. to
about 300° C. under superatmospheric pressure, while removing
water from the reaction zone, to form an esterification product mixture
comprising bis(4-methyl-cyclohexyl)methyl)terephthalate and unreacted
(4-methylcyclohexyl)methanol; [0006] (ii). contacting the esterification
product mixture with hydrogen in a first hydrogenation zone in the
presence of a catalyst effective for hydrogenation of an aromatic ring to
produce a liquid effluent comprising
bis(4-methylcyclohexyl)-methyl)cyclohexane-1,4-dicarboxylate; [0007]
(iii). contacting the effluent from the first hydrogenation zone with
hydrogen in the presence of an ester hydrogenation catalyst in a second
hydrogenation zone to produce a hydrogenation product comprising
1,4-cyclohexanedimethanol, 4,4'-oxybis(methylene)bis(methylcyclohexane),
and (4-methylcyclohexyl)methanol that was present in the esterification
product mixture, released during the hydrogenation of the
bis(4-methylcyclohexyl)methyl) cyclohexane-1,4-dicarboxylate, and
additionally produced as a by-product and; [0008] (iv) recycling at least
a portion of the (4-methylcyclohexyl)methanol from step (iii) to step
(i). In the process of the invention, terephthalic acid is esterified
with (4-methylcyclohexyl)-methanol (abbreviated herein as "MCHM"), which
is a by-product of the CHDM hydrogenation process, to produce
bis(4-methylcyclohexyl)methyl) terephthalate that is then hydrogenated to
CHDM. The MCHM released during the ester hydrogenation step, therefore,
does not introduce any new impurities into the hydrogenation process and
can be recycled to the esterification step of the process.

[0009] Our inventive process also provides a simplified method of
purification of the CHDM hydrogenation product mixture. Thus, another
embodiment of the invention is a process for the preparation of
1,4-cyclohexanedimethanol, comprising: [0010] (i). contacting
bis(4-methylcyclohexyl)methyl) terephthalate with hydrogen in a first
hydrogenation zone in the presence of a catalyst effective for
hydrogenation of an aromatic ring to produce a liquid effluent comprising
bis(4-methylcyclohexyl)-methyl) cyclohexane-1,4-dicarboxylate; [0011]
(ii). contacting the effluent from the first hydrogenation zone with
hydrogen in the presence of an ester hydrogenation catalyst in a second
hydrogenation zone to produce a hydrogenation product comprising
1,4-cyclohexanedimethanol, 4,4'-oxybis(methylene)bis(methylcyclohexane),
and (4-methylcyclohexyl)methanol; [0012] (iii). distilling the
hydrogenation product from step (ii) to recover a distillate comprising a
majority of the (4-methylcyclohexyl)methanol in the hydrogenation product
and a distillation bottoms comprising a majority of the
1,4-cyclohexane-dimethanol and
4,4'-oxybis(methylene)bis(methylcyclohexane) in the hydrogenation
product; [0013] (iv). allowing the distillation bottoms to form a lower
layer comprising a majority of the 1,4-cyclohexanedimethanol in the
distillation bottoms and a upper layer comprising a majority of the
4,4'-oxybis(methylene)bis(methylcyclohexane) in the distillation bottoms;
and [0014] (v). separating the upper and lower layers of step (iv) and
recovering the 1,4-cyclo-hexanedimethanol from the lower layer by
distillation. After removal of at least a portion of the MCHM present in
the crude CHDM hydrogenation mixture, the distillation bottoms separates
into an upper layer containing the diether of MCHM and many of the
impurities present in the hydrogenation product and a lower layer
comprising most of the CHDM product. Most of the by-products produced
during the hydrogenation step, therefore, can be removed by a simple
separation of the upper and lower layers.

[0015] The esterification and purification steps of our process can be
combined to provide an integrated process for CHDM in which the MCHM
by-product from the hydrogenation step is recycled to the TPA
esterification step as the alcohol feedstock. Yet another aspect of the
invention, therefore, is a process for the preparation of a
1,4-cyclohexanedimethanol from terephthalic acid, comprising: [0016]
(i). contacting terephthalic acid and (4-methylcyclohexyl)methanol in a
mole ratio of alcohol to acid of at least 2:1, in a reaction zone at a
temperature of about 200° C. to about 300° C. under
superatmospheric pressure, while removing water from the reaction zone,
to form an esterification product mixture comprising
bis(4-methyl-cyclohexyl)methyl)terephthalate and unreacted
(4-methylcyclohexyl)methanol; [0017] (ii). contacting the esterification
product mixture with hydrogen in a first hydrogenation zone in the
presence of a catalyst effective for hydrogenation of an aromatic ring to
produce a liquid effluent comprising
bis(4-methylcyclohexyl)-methyl)cyclohexane-1,4-dicarboxylate; [0018]
(iii). contacting the effluent from the first hydrogenation zone with
hydrogen in the presence of an ester hydrogenation catalyst in a second
hydrogenation zone to produce a hydrogenation product comprising
1,4-cyclohexanedimethanol, 4,4'-oxybis(methylene)bis(methylcyclohexane),
and (4-methylcyclohexyl)methanol; [0019] (iv). distilling the
hydrogenation product from step (iii) to recover a distillate comprising
a majority of the (4-methylcyclohexyl)methanol in the hydrogenation
product and a distillation bottoms comprising a majority of the
1,4-cyclohexane-dimethanol and
4,4'-oxybis(methylene)bis(methylcyclohexane) in the hydrogenation
product; [0020] (v). allowing the distillation bottoms to form an lower
layer comprising a majority of the 1,4-cyclohexanedimethanol in the
distillation bottoms and a upper layer comprising a majority of the
4,4'-oxybis(methylene)bis(methylcyclohexane) in the distillation bottoms;
[0021] (vi). separating the upper and lower layers of step (iv) and
recovering the 1,4-cyclo-hexanedimethanol from the lower layer by
distillation; and [0022] (vii) recycling at least a portion of the
(4-methylcyclohexyl)methanol from step (iv) to step (i).

DETAILED DESCRIPTION

[0023] The present invention provides a process for the preparation of
1,4-cyclo-hexanedimethanol by esterifying terephthalic acid (abbreviated
herein as "TPA") with (4-methylcyclohexyl)methanol ("MCHM") and
hydrogenating this ester to CHDM. In a general embodiment, the invention
provides a process for the preparation of 1,4-cyclo-hexanedimethanol from
terephthalic acid comprising: [0024] (i). contacting terephthalic acid
and (4-methylcyclohexyl)methanol in a reaction zone at a temperature of
about 200° C. to about 300° C. under superatmospheric
pressure, while removing water from the reaction zone, to form an
esterification product mixture comprising bis(4-methylcyclohexyl)methyl)
terephthalate, [0025] (ii). contacting the esterification product mixture
with hydrogen in a first hydrogenation zone in the presence of a catalyst
effective for hydrogenation of an aromatic ring to produce a liquid
effluent comprising
bis(4-methylcyclohexyl)-methyl)cyclohexane-1,4-dicarboxylate; [0026]
(iii). contacting the effluent from the first hydrogenation zone with
hydrogen in the presence of an ester hydrogenation catalyst in a second
hydrogenation zone to produce a hydrogenation product comprising
1,4-cyclohexanedimethanol, 4,4'-oxybis(methylene)bis(methylcyclohexane),
and (4-methylcyclohexyl)methanol, and; [0027] (iv). recycling at least a
portion of the (4-methylcyclohexyl)methanol from step (iii) to step (i).
The MCHM used as a starting material for our process is produced as a
by-product in the production of 1,4-cyclohexanedimethanol. Thus, because
the esterification process does not introduce any new materials (e.g.,
methanol to make dimethyl terephthalate) into the overall CHDM process,
our novel process reduces the amount equipment needed for the preparation
of 1,4-cyclohexanedimethanol from terephthalic acid and simplifies the
purification of the final product. The process of the invention also can
be used for the preparation of 1,3-cyclohexanedimethanol from isophthalic
acid.

[0028] Unless otherwise indicated, all numbers expressing quantities of
ingredients, properties such as molecular weight, reaction conditions,
and so forth used in the specification and claims are to be understood as
being modified in all instances by the term "about." Accordingly, unless
indicated to the contrary, the numerical parameters set forth in the
following specification and attached claims are approximations that may
vary depending upon the desired properties sought to be obtained by the
present invention. At the very least, each numerical parameter should at
least be construed in light of the number of reported significant digits
and by applying ordinary rounding techniques. Further, the ranges stated
in this disclosure and the claims are intended to include the entire
range specifically and not just the endpoint(s). For example, a range
stated to be 0 to 10 is intended to disclose all whole numbers between 0
and 10 such as, for example 1, 2, 3, 4, etc., all fractional numbers
between 0 and 10, for example 1.5, 2.3, 4.57, 6.1113, etc., and the
endpoints 0 and 10. Also, a range associated with chemical substituent
groups such as, for example, "C1 to C5 hydrocarbons," is intended to
specifically include and disclose C1 and C5 hydrocarbons as well as C2,
C3, and C4 hydrocarbons.

[0029] Notwithstanding that the numerical ranges and parameters setting
forth the broad scope of the invention are approximations, the numerical
values set forth in the specific examples are reported as precisely as
possible. Any numerical value, however, inherently contains certain
errors necessarily resulting from the standard deviation found in their
respective testing measurements.

[0030] As used in the specification and the claims, the singular forms
"a," "an" and "the" include their plural referents unless the context
clearly dictates otherwise. For example, reference to a "promoter" or a
"reactor" is intended to include the one or more promoters or reactors.
References to a composition or process containing or including "an"
ingredient or "a" step is intended to include other ingredients or other
steps, respectively, in addition to the one named.

[0031] The terms "containing" or "including," are synonymous with the term
"comprising," and is intended to mean that at least the named compound,
element, particle, or method step, etc., is present in the composition or
article or method, but does not exclude the presence of other compounds,
catalysts, materials, particles, method steps, etc., even if the other
such compounds, material, particles, method steps, etc., have the same
function as what is named, unless expressly excluded in the claims.

[0032] It is also to be understood that the mention of one or more method
steps does not preclude the presence of additional method steps before or
after the combined recited steps or intervening method steps between
those steps expressly identified. Moreover, the lettering of process
steps or ingredients is a convenient means for identifying discrete
activities or ingredients and the recited lettering can be arranged in
any sequence, unless otherwise indicated.

[0033] The esterification step of our process comprises contacting
terephthalic acid with MCHM in a reaction zone, under elevated
temperatures and pressures, and removing the water produced in the
esterification from the reaction zone as the reaction progresses. The
molar ratio of alcohol to acid that can be used is typically at least
2:1. For example, the ratio of MCHM to terephthalic acid can be about 2:1
to about 10:1. Some additional examples of molar ratios of alcohol to
acid in the esterification step include about 2:1 to about 9:1; about 2:1
to about 8:1; about 2:1 to about 7:1; about 2:1 to about 5:1; about 2:1
to about 4:1; and about 2:1 to about 3:1.

[0034] It is advantageous to remove the water produced by the
esterification reaction in order to improve the rate of the reaction and
the conversion to the terephthalic acid diester. Removal of the water may
be accomplished by any conventional means known to persons skilled in the
art such as, for example, by distillation, membrane separation, the use
of absorbents, or combinations thereof. For example, the water of
reaction may be removed by simple distillation from the esterification
reaction or by azeotropic distillation with MCHM. With azeotropic
distillation, the MCHM/water azeotrope is allowed to separate into an
MCHM layer and a water layer, the water layer removed, and the MCHM layer
returned to the esterification reaction. In another example, the water of
the reaction can be removed by azeotropic distillation by adding a
solvent to the esterification reaction mixture that forms an azeotrope
with water under the esterification conditions of temperature and
pressure. The use of azeotropic solvents, however, will, in general,
require additional steps to remove the azeotropic solvent from either the
esterification or CHDM reaction product mixture. The water of reaction
may also be removed by exposing or passing the reaction mixture through
an adsorbent. The removal of the water of reaction from the reaction zone
also may be assisted by passing an inert gas through the TPA-MCHM
reaction mixture in the reaction zone and condensing the water from the
inert gas stream after it exits the reactor. Nitrogen is an example of an
appropriate inert gas. The inert gas typically is fed below the surface
of the TPA-MCHM reaction mixture by means of a conventional conduit or
via a gas sparging device. The inert gas may be fed intermittently or
discontinuously. For example, the inert gas can be fed continuously at
the commencement of the esterification reaction. The amount of gas passed
through the TPA-MCHM reaction mixture may vary significantly but
typically is in the range of about 2 to 5 volumes of gas per volume of
reaction mixture per hour. It will be apparent to persons skilled in the
art that numerous variations and combinations of these methods are
possible.

[0035] The esterification may be carried out by the joint addition of the
TPA and MCHM or by the incremental addition of one of the feed substrate
materials to the other. For example, the terephthalic acid can be added
incrementally to a reaction zone that contains the full amount of the
alcohol to be used in the esterification reaction. Alternatively, the
MCHM may be added incrementally to the full or partial amount of TPA that
is to be used in the esterification process. The term "incrementally," as
used herein, is intended to have its plain meaning of adding the TPA
component or MCHM component to the reaction zone in one or more
increments or portions to increase the amount of the MCHM or TPA
component in the reaction zone. The increments do not have to be equal in
size. For example, one increment may contain 90% of the total amount of
TPA component and a second increment may contain the remaining 10%. The
increments may be added stepwise in discrete portions, continuously, or
in a combination thereof. Therefore, the term "incrementally," as used in
the description and claims, is intended to include both continuous and
stepwise additions of the MCHM and/or TPA components. Thus,
"incrementally" means that, over the duration of the entire process, the
MCHM or TPA components can be added to the reaction zone continuously,
stepwise in 2 or more stages or discrete steps, or in a combination of
continuous and stepwise addition. Thus, in one embodiment of the
invention, the TPA component is added to the reaction zone in 2 or more
stages. In another embodiment, the TPA component is added to the reaction
zone continuously.

[0036] The TPA and MCHM are contacted in a reaction zone at a temperature
of about 200 to about 300° C. under superatmospheric pressure. For
example, the TPA and MCHM can be contacted at a temperature of about 220
to about 280° C. at a pressure of about 1.4 bar gauge to about 50
bar gauge. Other examples of pressure and temperature that the
esterification step may be operated at about 230 to about 280° C.
at a pressure of about 1.4 to about 21 bar gauge, and about 240 to about
270° C. at about 1.4 to about 6.9 bar gauge.

[0037] The TPA and MCHM are reacted while removing water from the reaction
mixture to form an esterification product mixture comprising
bis(4-methylcyclohexyl)-methyl)terephthalate, represented by formula (I),
and unreacted (4-methylcyclohexyl)-methanol. In one embodiment of the
process, the TPA and MCHM are heated together with water removal until a
product mixture having a desired conversion is obtained.

##STR00001##

The desired conversion can be determined by conventional analytical
methods known to persons skilled in the art such as, for example, by NMR,
titration (i.e., acid number), gas chromatography, and liquid
chromatography. Acid number may be determined by titration of the
esterification product mixture with potassium hydroxide and is reported
as mg of potassium hydroxide consumed for each gram of esterification
product mixture (mg KOH/g esterification product mixture). The
esterification product mixture will typically have an acid number of
about 10 mg KOH or less/gram of esterification product mixture to reduce
poisoning and deactivation of any hydrogenation catalysts in the
subsequent steps of the process. Additional examples of acid number
values for the esterification product mixture are about 8 mg KOH or
less/gram of esterification product mixture, about 5 mg KOH or less, and
about 3 mg KOH or less. The esterification step may also be monitored by
measuring the water evolved from the reaction mixture, computer modeling
of the reaction rate, or any other means capable of determining the
concentration of reactants or products in the esterification product
mixture.

[0038] The MCHM used to esterify TPA in the process of the invention is
produced as a by-product in the production of CHDM by the multistage
hydrogenation of TPA diesters that proceeds by hydrogenation of the
aromatic ring produce the corresponding 1,4-cyclo-hexanedicarboxylate
diester, which is further hydrogenated to produce CHDM. In one embodiment
of our invention, therefore, the MCHM used in the esterification reaction
with TPA can be recovered and recycled from a process for the preparation
of CHDM by hydrogenation of bis(4-methylcyclohexyl)methyl) terephthalate.
The MCHM used in the esterification may also include unreacted MCHM that
has been recovered and recycled from the esterification step of our CHDM
process. In one embodiment of our invention, the MCHM used to esterify
TPA, recycled to the esterification step, or a combination thereof,
further comprises one or more additional alcohols having 4 to 20 carbon
atoms in minor or major quantities. In another embodiment, the one or
more additional alcohols comprise 1-butanol, 2-butanol, 2-ethylhexanol,
cyclohexanol, benzyl alcohol, 1-hexanol, 1-pentanol, 1-octanol,
1-nonanol, 1-decanol, or combinations thereof. In yet another embodiment,
the MCHM used to esterify TPA in step (i) contains from 0 to than 5
weight percent of the one or more additional alcohols based on the total
amount of MCHM used in the esterification step. Some other examples of
the concentration of the additional alcohols are 0 to less than 3 weight
percent, 0 to less than 2 weight percent, 0 to less than 1 weight
percent, and 0 to less than 0.5 weight percent. In still another
embodiment, the MCHM used to esterify TPA in step (i) contains greater
than 10 weight percent of one or more additional alcohols based on the
total amount of MCHM used in the esterification step.

[0039] The esterification reaction may be carried out in the presence or
absence of an exogenous esterification catalyst, i.e., a catalyst other
than terephthalic acid that is added to the reaction mixture for the
purpose of increasing the rate of the esterification reaction. Any
esterification catalyst that is known in art may be used. For example,
the TPA and MCHM can be contacted in the presence of a catalyst
comprising compounds of titanium, magnesium, aluminum, boron, silicon,
tin, zirconium, zinc, antimony, manganese, calcium, vanadium, sulfuric
acid, p-toluene sulfonic acid, methane sulfonic acid, or phosphoric acid.
For example, acetates, chlorides, nitrates, sulfates, oxides and
alkoxides of metals such as zinc, manganese, tin, titanium, antimony,
cobalt and lithium may be used. Buffering compounds, such as alkaline
salts of organic acids, can be included with the catalysts if desired.

[0040] Some representative examples of catalysts that may be used in the
esterification step include, but are not limited to, titanium, zirconium,
and tin alcoholates, carboxylates, and chelates; zinc acetate; zinc
oxide, antimony oxide, stannous oxalate, zinc acetyl acetonate, calcium
oxide, and manganese oxide. Titanium and zirconium catalysts are
frequently used for esterification of terephthalic acid. Some typical
titanium alcoholates which can be used as catalysts include tetramethyl
titanates, tetraethyl titanates, tetrapropyl titanates, tetraisopropyl
titanates, tetrabutyl titanates, tetrapentyl titanates, tetrahexyl
titanates, and tetraoctyl titanates. The alkoxy groups on the titanium
atom can all be the same or they can be different. The zirconium
counterparts of the above alcoholates can be substituted in whole or in
part as catalysts. Typically, the concentration of catalyst can be about
0.03 to about 1 weight percent, based on total weight of esterification
reaction mixture.

[0041] Although the esterification process may be carried out in the
presence of a catalyst, we have unexpectedly found that TPA has a high
(i.e., about 1% at 200° C.) solubility in MCHM, which allows the
esterification reaction to proceed smoothly without added catalysts.
Thus, in one embodiment of the invention, the TPA and MCHM are contacted
in the absence of an exogenous catalyst. Conducting the esterification
reaction step in the absence of a catalyst avoids the need for additional
purification steps to remove catalyst residues which can poison the
hydrogenation catalysts or catalyze the formation of color bodies and
other undesirable by-products in the subsequent steps of the instant
process.

[0042] The process of the present invention may be carried out in a batch,
semi-continuous or continuous mode. In the batch mode, for example, an
agitated pressure vessel may be charged with TPA and MCHM, heated and
pressurized and the esterification is carried out under reflux conditions
while removing water from the reaction mixture. The high solubility of
TPA in MCHM, as noted above, also allows the esterification to be
conducted in a continuous mode with lower residence times and smaller
reactors than would be typically used for the esterification of TPA with
other alcohols. Any alcohol that is removed from the reaction mixture
with the water can be recovered and fed back to the reaction vessel over
the course of the process. At the conclusion of the reaction, the
esterification product mixture can be used in the subsequent
hydrogenation step as is or the unreacted MCHM may recovered from
esterification product mixture by distillation or any conventional means
known to persons skilled in the art and recycled. Continuous operation
involves continuously or intermittently feeding TPA and MCHM to and
continuously or intermittently removing alcohol, water and
product-containing reaction mixture from a pressure vessel maintained at
a predetermined temperature, pressure and liquid level. It will be
apparent to those skilled in the art that other reactor schemes may be
used with this invention. For example, the esterification reaction can be
conducted in a plurality of reaction zones, in series, in parallel, or it
may be conducted batch wise or continuously in a tubular plug flow
reaction zone or series of such zones with recycle of unconsumed feed
substrate materials if required. For example, the esterification reaction
mixture may be fed to one or more secondary reaction vessels wherein
conversion of TPA and/or TPA half-ester to the diester product is
completed.

[0043] The esterification product mixture typically can comprise at least
50 weight percent of bis(4-methylcyclohexyl)methyl) terephthalate based
on the total weight of the esterification product mixture, although lower
concentrations may be present. Other examples of weigh percentages of
bis(4-methylcyclohexyl)methyl) terephthalate in the esterification
product mixture are at least 60 weight percent, at least 70 weight
percent, at least 80 weight percent, and at least 90 weight percent.

[0044] The esterification product mixture can be contacted with hydrogen
in a first hydrogenation zone in the presence of a catalyst effective for
hydrogenation of an aromatic ring to produce a liquid effluent that
comprises bis(4-methylcyclohexyl)methyl) cyclohexane-1,4-dicarboxylate,
represented by formula (II):

##STR00002##

[0045] The hydrogenation of the esterification product mixture may be
carried out over a temperature range of about 150° to 350°
C. Generally, higher temperatures favor carbon monoxide formation and,
therefore, the use of temperatures in the upper part of the range may
require means for removing carbon monoxide from the hydrogenation zone
such as, for example, by purging all, or substantially all, of the
hydrogen effluent of the process. Other examples of temperatures for the
hydrogenation of the esterification product mixture include about 160 to
about 300° C., about 180 to about 300° C., about 170 to
about 280° C., about 170 to about 260° C., and about
170° C. to about 240° C. The process may be operated in
either an adiabatic or isothermal process.

[0046] The hydrogenation of the esterification product mixture may be
performed within a pressure range of about 50 to 400 bar gauge. In
another example, the pressure of the hydrogenation may range from about
50 to about 170 bar gauge.

[0047] The hydrogenation of the esterification product mixture can be
carried out in a batch, semi-continuous or continuous mode using
conventional chemical processing techniques. In another embodiment of the
present invention, the process comprises a combination of two or more of
batch, semi-continuous or continuous modes. In certain embodiments, the
mode of operation may be a continuous process in which the esterification
product mixture is passed over and through one or more fixed beds of
catalyst in a "trickle bed" manner and all or a portion of the
bis(4-methylcyclohexyl)-methyl)terephthalate is converted to
bis(4-methylcyclohexyl)methyl) cyclohexane- 1,4-dicarboxylate (II). For
example, a portion of the effluent from one or more fixed catalyst beds,
comprising bis(4-methylcyclohexyl)methyl) cyclohexane-1,4-dicarboxylate
(II) may be recycled to the feed port of the reactor where it serves as a
solvent for the esterification product feed. In another embodiment, the
esterification product mixture may be supplied to the hydrogenation zone
at a rate which will result in substantially complete conversion of the
reactant to the cyclohexanedicarboxylate product. In some embodiments of
the present invention, one or more inert, non-aromatic compounds, which
are liquid under the operating conditions employed, may be used as a
solvent or solvent mixture. Examples of suitable solvents include, but
not limited to, alcohols, such as MCHM and CHDM, and other esters.

[0048] The most suitable LHSV (LHSV, liquid hourly space velocity is the
unit volume of reactant fed per hour per unit volume catalyst) for the
esterification product mixture feed is dependent upon the particular
temperature and pressure used which, as mentioned hereinabove, can depend
upon the flow rate and/or purity of the hydrogen. In trickle bed
operation, the liquid hourly space velocity of the esterification product
mixture feed may be in the range of about 0.1 to 10 with a preferred
range of 0.5 to 5. In some embodiments the lower limit of the LHSV of the
esterification product mixture feed may be 0.1 or 0.2 or 0.3 or 0.4 or
0.5 or 0.6 or 0.7 or 0.8 or 0.9 or 1.0 or 2.0 or 3.0 or 4.0 or 5.0 or 6.0
or 7.0 or 8.0 or 9.0. In some embodiments the upper limit of the LHSV of
the esterification product mixture feed may be 0.2 or 0.3 or 0.4 or 0.5
or 0.6 or 0.7 or 0.8 or 0.9 or 1.0 or 2.0 or 3.0 or 4.0 or 5.0 or 6.0 or
7.0 or 8.0 or 9.0 or 10.0. The range of the LHSV of the esterification
product mixture feed may be a combination of any lower limit with any
upper limit listed above.

[0049] The LHSV for the total liquid flow (esterification product mixture
feed plus solvent) may be in the range of 1 to 40. In some embodiments
the lower limit of the LHSV of the total liquid flow may be 1.0 or 2.0 or
3.0 or 4.0 or 5.0 or 6.0 or 7.0 or 8.0 or 9.0 or 10 or 15 or 20 or 25 or
30 or 35. In some embodiments, the upper limit of the LHSV of the total
liquid flow may be 2.0 or 3.0 or 4.0 or 5.0 or 6.0 or 7.0 or 8.0 or 9.0
or 10 or 15 or 20 or 25 or 30 or 35 or 40. The range of the LHSV of the
total liquid flow may be a combination of any lower limit with any upper
limit listed above.

[0050] The hydrogen gas used in the process may comprise fresh gas or a
mixture of fresh gas and recycle gas. The hydrogen gas can be a mixture
of hydrogen, optional minor amounts of components such as CO and
CO2, and inert gases, such as argon, nitrogen, or methane,
containing at least about 70 mole % of hydrogen. For example, the
hydrogen gas can contain at least 90 mole % or, in another example, at
least 97 mole %, of hydrogen. The hydrogen gas may be obtained from any
of the common sources well known in the art such as, for example, by
partial oxidation or steam reforming of natural gas. Pressure swing
absorption can be used if a high purity hydrogen gas is desired. If gas
recycle is utilized in the process, then the recycle gas will normally
contain minor amounts of one or more products of the hydrogenation
reaction which have not been fully condensed in the product recovery
stage downstream from the hydrogenation zone. Thus, when using gas
recycle in the process of the invention, the gas recycle stream will
typically contain a minor amount of an alkanol, e.g., MCHM. Hydrogen is
typically fed to the reactor in excess of the stoichiometric quantity and
normally is purged from the system. The rate of hydrogen purge is
dependent on the temperature and pressure at which the process is
operated.

[0051] The hydrogenation of the esterification product mixture may be
catalyzed by any catalyst that is effective for the reduction of an
aromatic ring. In certain embodiments for example, the catalyst can
comprise a Group VIII metal (Groups 8, 9, and 10 according to IUPAC
numbering) deposited on a catalyst support material comprising alumina,
silica-alumina, titania, zirconia, chromium oxides, graphite, silicon
carbide, or combinations thereof. Examples of the Group VIII metals that
may be used include, but are not limited to, palladium, platinum,
ruthenium, nickel and combinations thereof. In one embodiment of the
present invention the total amount of Group VIII metal present may be
about 0.1 to 10 weight percent based on the total weight of the catalyst.
The lower limit of the weight percent of the Group VIII metal may be 0.1
or 0.2 or 0.3 or 04 or 0.5 or 0.6 or 0.7 or 0.8 or 0.9 or 1.0 or 2.0 or
3.0 or 4.0 or 5.0 or 6.0 or 7.0 or 8.0 or 9.0. The upper limit of the
weight percent of the Group VIII metal may be 0.2 or 0.3 or 04 or 0.5 or
0.6 or 0.7 or 0.8 or 0.9 or 1.0 or 2.0 or 3.0 or 4.0 or 5.0 or 6.0 or 7.0
or 8.0 or 9.0 or 10.0. The range of the weight percent of the Group VIII
metal may be any combination of any lower limit with any upper limit. For
example, the catalyst can comprise palladium supported on alumina. In
another embodiment of the present invention the catalyst can comprise
about 0.5 to 5 weight percent palladium wherein the weight percentages
are based on the total weight of the catalyst, e.g., the total weight of
the support material plus the Group VIII metal. In another embodiment of
the present invention the catalysts further comprise about 0.5 to 5
weight percent palladium, optionally in combination with about 0.01 to 2
weight percent nickel, ruthenium or a mixture thereof, wherein the weight
percentages are based on the total weight of the catalyst, e.g., the
total weight of the support material plus the metals. The catalyst may be
in any conventional form such as, for example, in the form of extrudates,
granules, and pellets for use in fixed-bed reactor processes and powder
for slurry processes. The shape of the supports may be, but are not limit
to, cylinders, spheres, stars or any type of multiple-lobe shapes.
Depending on the particular support material employed and/or the method
used to prepare a catalyst, the Group VIII metal may be deposited
primarily on the surface of the support or distributed substantially
throughout the support.

[0052] The catalysts may be prepared by conventional techniques such as
impregnation of one or more Group VIII metals or Group VIII metal
compounds on or into the support material. The Group VIII metals may be
provided as zero valence metals or as oxidized metals in the form of
compounds such as salts of inorganic or organic acids and organometallic
complexes. In one embodiment, the support materials may be impregnated
with one or more Group VIII metals by immersing the support material in a
solution of a Group VIII metal compound in a suitable solvent such as
water or an organic solvent. The support material then is dried and the
metal compound is reduced to a Group VIII metal.

[0053] In one example of the invention, the esterification product mixture
is contacted with hydrogen at a temperature of about 150 to about
350° C. and a pressure of about 50 to about 400 bar gauge and in
the presence of a catalyst comprising palladium, platinum, nickel,
ruthenium or combinations thereof deposited on a catalyst support
material. In another embodiment, the esterification product mixture may
be contacted with hydrogen at a temperature of about 180 to about
300° C. and a pressure of about 50 to about 170 bar gauge, in the
presence of a catalyst comprising palladium, ruthenium, or combinations
thereof, deposited on a catalyst support material comprising alumina,
silica-alumina, titania, zirconia, chromium oxides, graphite, silicon
carbide, or combinations thereof. It will be apparent to persons skilled
in the art that other combinations of temperature, pressure, and
catalysts may be used.

[0054] The hydrogenation of the esterification product mixture in the
first hydrogenation zone produces a liquid effluent comprising
bis(4-methylcyclohexyl)-methyl)cyclohexane-1,4-dicarboxylate and,
optionally, (4-methylcylohexyl)methanol. The liquid effluent is contacted
with hydrogen in the presence of an ester hydrogenation catalyst in a
second hydrogenation zone to produce a hydrogenation product comprising
1,4-cyclohexanedimethanol, 4,4'-oxybis(methylene)bis(methylcyclohexane),
represented by formula (III) and abbreviated to hereinafter as
"MCHM-diether," and (4-methylcyclohexyl)methanol. The MCHM can comprise
MCHM that was present in the esterification product mixture, released
during the hydrogenation of the

##STR00003##

bis(4-methylcyclohexyl)methyl) cyclohexane-1,4-dicarboxylate, and
additionally produced as a by-product.

[0055] The hydrogenation conditions of pressure and temperature for the
liquid effluent from the first hydrogenation zone may be varied depending
not only on one another but also on the activity of the catalyst, the
mode of operation, selectivity considerations, and the desired rate of
conversion. The process typically is conducted at temperatures in the
range of about 160° C. to about 300° C. and pressures in
the range of about 40 to about 400 bar gauge (abbreviated herein as
"barg"). Further examples of temperatures and pressures at which the
process of the invention may be operated are about 175 to about
300° C. at about 200 to about 380 barg, and about 200 to about
250° C. at about 300 to about 350 barg. While rates and
conversions generally also increase with increasing pressure, the energy
costs for compression of hydrogen, as well as the increased cost of
high-pressure equipment generally make the use of the lowest pressure
practical advantageous.

[0056] The process of this invention may be carried out in the absence or
presence of an inert solvent, i.e., a solvent for the
cyclohexanedicarboxylate ester being hydrogenated which does not affect
significantly the activity of the catalyst and does not react with the
hydrogenation product or products. Examples of such solvents include
alcohols such as ethanol and lauryl alcohol; glycols such as mono-, di-
and tri-ethylene glycol; hydrocarbons such as hexane, cyclohexane, octane
and decane; and aromatic ethers such as diphenyl ether, etc. It is often
economically advantageous, however, to conduct the process in the absence
of solvent and use the neat, molten cyclohexanedicarboxylate ester alone
or as a mixture with 1,4-cyclohexanedimethanol and other hydrogenation
products as the feed to the process.

[0057] The hydrogenation of the liquid effluent containing the
cyclohexanedicarboxylate ester (II) may be carried out as a batch,
semi-continuous or continuous process and may utilize a variety of
reactor types. Examples of suitable reactor types include, but are not
limited to, stirred tank, continuous stirred tank, slurry, tubular, fixed
bed, and trickle bed. A plurality of reactors, stages, or hydrogenation
zones may be used. For economic and operability reasons, the process is
advantageously operated as a continuous process. Continuous operation may
utilize a fixed bed with a larger particle size of catalyst such as, for
example, granules, pellets, various multilobal shaped pellets, rings, or
saddles that are well known to skilled persons in the art. As an example
of a continuous process, the catalyst bed may be fixed in a high
pressure, tubular or columnar reactor and the liquid effluent from the
first hydrogenation zone, dissolved in an inert solvent if necessary or
desired, fed continuously into the top of the bed at elevated pressure
and temperature, and the crude hydrogenation product removed from the
base of the reactor. Alternatively, it is possible to feed the liquid
effluent containing the cyclohexanedicarboxylate ester (II) into the
bottom of the bed and remove the crude product from the top of the
reactor. It is also possible to use 2 or more catalyst beds or
hydrogenation zones connected in parallel or in series to improve
conversion, to reduce the quantity of catalyst, or to bypass a catalyst
bed for periodic maintenance or catalyst removal. Another mode of
continuous operation utilizes a slurry of the catalyst in an agitated
pressure vessel which is equipped with a filter leg to permit continuous
removal of a solution of product in unreacted ester and/or an inert
solvent. In this manner a liquid reactant or reactant solution can be
continuously fed to and product solution continuously removed from an
agitated pressure vessel containing an agitated slurry of the catalyst.

[0058] In one example, a portion of the hydrogenation product from one or
more fixed catalyst beds, comprising CHDM may be recycled to the feed
port of the reactor where it serves as a solvent for the liquid effluent
feed containing the cyclohexanedicarboxylate ester (II). In another
embodiment, the liquid effluent feed may be supplied to the hydrogenation
zone at a rate which will result in substantially complete conversion of
the cyclohexanedicarboxylate ester (II) to the CHDM product. In some
embodiments of the present invention, one or more inert, non-aromatic
compounds, which are liquid under the operating conditions employed, may
be used as a solvent or solvent mixture. Examples of suitable solvents
include, but not limited to, alcohols, such as MCHM and CHDM, and other
esters.

[0059] The process may be conducted in the liquid phase, the vapor phase,
or as combination of the liquid and vapor phase. For example, the process
may be carried in the vapor phase as described, for example, in U.S. Pat.
No. 5,395,987. In one example of a vapor phase operation, the process of
the invention may be operated using vaporous feed conditions by feeding
the liquid effluent containing the cyclohexanedicarboxylate ester (II) to
a hydrogenation zone comprising the ester hydrogenation catalyst in
essentially liquid free vaporous form. Hence, the feed stream is
introduced into the hydrogenation zone at a temperature which is above
the dew point of the mixture. The process may be operated so that vapor
phase conditions will exist throughout the hydrogenation zone. Such a
vapor phase process often has the advantage of lower operating pressures
in comparison to liquid phase process which can reduce the construction
and operating costs of a commercial plant.

[0060] The most suitable LHSV for the liquid effluent from the first
hydrogenation zone is dependent upon the particular temperature and
pressure used which, as mentioned hereinabove, can depend upon the flow
rate and/or purity of the hydrogen. In trickle bed operation, the liquid
hourly space velocity of the liquid effluent feed may be in the range of
about 0.1 to 10 with a preferred range of 0.5 to 5. In some embodiments
the lower limit of the LHSV of the liquid effluent feed may be 0.1 or 0.2
or 0.3 or 0.4 or 0.5 or 0.6 or 0.7 or 0.8 or 0.9 or 1.0 or 2.0 or 3.0 or
4.0 or 5.0 or 6.0 or 7.0 or 8.0 or 9.0. In some embodiments the upper
limit of the LHSV of the liquid effluent feed may be 0.2 or 0.3 or 0.4 or
0.5 or 0.6 or 0.7 or 0.8 or 0.9 or 1.0 or 2.0 or 3.0 or 4.0 or 5.0 or 6.0
or 7.0 or 8.0 or 9.0 or 10.0. The range of the LHSV of the liquid
effluent feed may be a combination of any lower limit with any upper
limit listed above.

[0061] The LHSV for the total liquid flow (liquid effluent feed plus
solvent) may be in the range of 1 to 40. In some embodiments the lower
limit of the LHSV of the total liquid flow may be 1.0 or 2.0 or 3.0 or
4.0 or 5.0 or 6.0 or 7.0 or 8.0 or 9.0 or 10 or 15 or 20 or 25 or 30 or
35. In some embodiments the upper limit of the LHSV of the total liquid
flow may be 2.0 or 3.0 or 4.0 or 5.0 or 6.0 or 7.0 or 8.0 or 9.0 or 10 or
15 or 20 or 25 or 30 or 35 or 40. The range of the LHSV of the total
liquid flow may be a combination of any lower limit with any upper limit
listed above.

[0062] The hydrogen gas used in the process may comprise fresh gas or a
mixture of fresh gas and recycle gas. The hydrogen gas can be a mixture
of hydrogen, optional minor amounts of components such as CO and
CO2, and inert gases, such as argon, nitrogen, or methane,
containing at least about 70 mole % of hydrogen. For example, the
hydrogen gas contains at least 90 mole % or, in another example, at least
97 mole %, of hydrogen. The hydrogen gas may be obtained from any of the
common sources well known in the art such as, for example, by partial
oxidation or steam reforming of natural gas. Pressure swing absorption
can be used if a high purity hydrogen gas is desired. If gas recycle is
utilized in the process, then the recycle gas will normally contain minor
amounts of one or more products of the hydrogenation reaction which have
not been fully condensed in the product recovery stage downstream from
the hydrogenation zone. Thus, when using gas recycle in the process of
the invention, the gas recycle stream will typically contain a minor
amount of an alkanol, e.g., MCHM. Hydrogen is typically fed to the
reactor in excess of the stoichiometric quantity and normally is purged
from the system. The rate of hydrogen purge is dependent on the
temperature and pressure at which the process is operated.

[0063] The hydrogenation of the cyclohexanedicarboxylate ester (III) in
the liquid effluent from the first hydrogenation zone may be catalyzed by
any catalyst that is effective for the reduction of esters to alcohols.
Typical ester hydrogenation catalysts include copper-containing catalysts
and Group VIII metal-containing catalysts. Examples of suitable
copper-containing catalysts include copper-on-alumina catalysts, copper
oxide, reduced copper oxide/zinc oxide catalysts, with or without a
promoter, manganese promoted copper catalysts, and reduced copper
chromite catalysts, with or without a promoter, while suitable Group VIII
(Groups 8, 9, and 10 according to IUPAC numbering) metal-containing
catalysts include platinum, palladium, nickel, and cobalt catalysts.
Suitable copper oxide/zinc oxide catalyst precursors include CuO/ZnO
mixtures wherein the Cu:Zn weight ratio ranges from about 0.4:1 to about
2:1. Promoted copper oxide/zinc oxide precursors include CuO/ZnO mixtures
wherein the Cu:Zn weight ratio ranges from about 0.4:1 to about 2:1 which
are promoted with from about 0.1% by weight up to about 15% by weight of
barium, manganese or a mixture of barium and manganese. Such promoted
CuO/ZnO mixtures include the Mn-promoted CuO/ZnO precursor. Suitable
copper chromite catalyst precursors include those wherein the Cu:Cr
weight ratio ranges from about 0.1:1 to about 4:1, preferably from about
0.5:1 to about 4:1. Promoted copper chromite precursors include copper
chromite precursors wherein the Cu:Cr weight ratio ranges from about
0.1:1 to about 4:1, preferably from about 0.5:1 to about 4:1, which are
promoted with from about 0.1% by weight up to about 15% by weight of
barium, manganese or a mixture of barium and manganese. Manganese
promoted copper catalyst precursors typically have a Cu:Mn weight ratio
of from about 2:1 to about 10:1 and can include an alumina support, in
which case the Cu:Al weight ratio is typically from about 2:1 to about
4:1. In certain embodiments for example, the catalyst can comprise a
Group VIII metal deposited on a catalyst support material comprising
alumina, silica-alumina, titania, zirconia, chromium oxides, graphite,
silicon carbide, or combinations thereof.

[0064] The ester hydrogenation catalyst may also comprise Raney metal
catalysts. The Raney metal catalyst may comprise any catalytically active
metal useful for the hydrogenation of cyclohexanedicarboxylate esters to
the corresponding cyclohexane-dimethanols. Exemplary Raney metals include
nickel, cobalt, copper, or combinations thereof. For example, the Raney
metal catalyst may comprise nickel. The term "Raney metal," as used
herein, means a metal produced by the "Raney" process, that is, a process
in which the metal catalyst is prepared by selective removal of one or
more components from an alloy and leaving the remaining metal behind as
the catalyst. The Raney process is described, for example, in U.S. Pat.
Nos. 1,628,190 and 6,284,703. The alloy components may be removed by any
method, e.g., dissolving out by chemical means or by volatilization, etc.
Typically, the Raney metal is produced by contacting an alloy of the
metal, containing leachable alloying components such as aluminum, zinc,
silicon, or a combination thereof, with sodium hydroxide. The catalytic
metal that remains is generally in a highly active porous or finely
divided state. The ratio by weight of Raney process metal to leachable
alloying component in the catalyst alloy may be in the range of about
10:90 to about 90:10, as is normally the case with Raney alloys. The
Raney catalyst may also comprise a metal binder which does not have to be
the same as the catalytically active metal present in the catalyst alloy.
Rather, it is possible to combine different Raney process metals with
each other as well as with promoter metals, in the catalyst alloy and as
binder, offering a further degree of freedom when adjusting the catalytic
properties to the particular catalytic process. For example, the binder
can be nickel, cobalt, copper, iron and, optionally, promoter metals.
Generally any of the metals used for making Raney metal catalysts are
suitable. The binder metal may be employed in an unreachable and
unadulterated form.

[0065] In one embodiment of the process of the invention, the liquid
effluent from the first hydrogenation zone is contacted with hydrogen at
a temperature of 160 to about 300° C. at a pressure of about 40 to
about 400 bar gauge in the presence of an ester hydrogenation catalyst
comprising at least one Group VIII metal, a copper-containing catalyst,
or a combination thereof. In another embodiment, the ester hydrogenation
catalyst comprises copper chromite, copper oxide, Raney nickel, Raney
cobalt, or combinations thereof, and is optionally promoted with zinc,
barium, calcium, manganese, magnesium, nickel, ruthenium, or lanthanum.
Other possible combinations of temperatures, pressures, and catalysts
will be apparent to persons having ordinary skill in the art.

[0066] The hydrogenation of the effluent from the first hydrogenation zone
produces a hydrogenation product comprising 1,4-cyclohexanedimethanol,
4,4'-oxybis(methylene)-bis(methylcyclohexane) (III), and
(4-methylcyclohexyl)methanol that was present in the esterification
product mixture, released during the hydrogenation of the
bis(4-methyl-cyclohexyl)methyl)cyclohexane-1,4-dicarboxylate, and
additionally produced as a by-product. The MCHM that is present in the
hydrogenation product can comprise MCHM produced as a by-product in
addition to unreacted MCHM that was present in and carried forth with the
esterification product mixture and MCHM that is released by the
hydrogenation of
bis(4-methylcyclohexyl)methyl)cyclohexane-1,4-dicarboxylate (II). It will
apparent to persons skilled in the art that the hydrogenation of 1 mole
of cyclohexanedicarboxylate ester (II) will produce 2 moles of MCHM and 1
mole of CHDM. Additional MCHM is produced as a by-product of the overall
hydrogenation of bis(4-methylcyclohexyl)methyl) terephthalate to CHDM.
Thus, the term "by-product," as used herein in reference to the MCHM
present in the hydrogenation products of the present invention, is
understood to mean the MCHM that is produced in the first and second
hydrogenation zones in addition to the unreacted MCHM present in
esterification product mixture and the MCHM released by the hydrogenation
of the cyclohexane-dicarboxylate ester (II).

[0067] The MCHM in the hydrogenation product from the second hydrogenation
zone can be recovered and recycled to the esterification step with
terephthalic acid. For example, the MCHM in the hydrogenation product can
be recovered by distillation of the hydrogenation product mixture.
Fractional distillation may be employed to improve the separation of the
various components of the hydrogenation product. The recovered and/or
recycled MCHM may further comprise one or more additional alcohols having
4 to 20 carbon atoms in minor or major quantities. Some representative
examples of additional alcohols that may be present in the recycled MCHM
are 1-butanol, 2-butanol, 2-ethylhexanol, cyclohexanol, benzyl alcohol,
1-hexanol, 1-pentanol, 1-octanol, 1-nonanol, 1-decanol, or combinations
thereof

[0068] Another embodiment of our invention is a process for the
preparation of 1,4-cyclohexanedimethanol from terephthalic acid,
comprising: [0069] (i). contacting terephthalic acid and
(4-methylcyclohexyl)methanol in a mole ratio of alcohol to acid of about
2:1 to about 5:1, in a reaction zone at a temperature of about
220° C. to about 280° C. in the absence of a exogenous
catalyst under superatmospheric pressure, while removing water from the
reaction zone, to form an esterification product mixture comprising
bis(4-methylcyclohexyl)methyl) terephthalate and unreacted
(4-methylcyclohexyl)methanol; [0070] (ii). contacting the esterification
product mixture with hydrogen in a first hydrogenation zone in the
presence of a palladium on alumina catalyst to produce a liquid effluent
comprising bis(4-methylcyclohexyl)methyl) cyclohexane- 1,4-dicarboxylate;
[0071] (iii). contacting the effluent from the first hydrogenation zone
with hydrogen in the presence of a copper chromite catalyst in a second
hydrogenation zone to produce a hydrogenation product comprising
1,4-cyclohexanedimethanol, 4,4'-oxybis-(methylene)bis(methylcyclohexane),
and (4-methylcyclohexyl)methanol; [0072] (iv). recovering the
(4-methylcyclohexyl)methanol from the hydrogenation product by
distillation; and [0073] (v). recycling at least a portion of the
(4-methylcyclohexyl)methanol to step (i).

[0074] For example, the hydrogenation of the effluent from the first
hydrogenation zone produces a hydrogenation product comprising
1,4-cyclohexanedimethanol, 4,4'-oxybis(methylene)bis(methylcyclohexane)
(III), and (4-methylcyclohexyl)methanol that was present in the
esterification product mixture, released during the hydrogenation of the
bis(4-methylcyclohexyl)methyl) cyclohexane-1,4-dicarboxylate, and
produced as a by-product. In one embodiment of the invention, all or a
portion of the (4-methylcyclo-hexyl)methanol that is contacted with the
terephthalic acid is recycled from step (v) of the above process. In
another embodiment, the amount of MCHM in the hydrogenation product of
step (iii) is sufficient to satisfy the (4-methylcyclohexyl)methanol
required for the esterification reaction with terephthalic acid in step
(i). In yet another embodiment, the above process is a continuous
process.

[0075] As described above, the MCHM may be recovered from the crude
hydrogenation product from the second hydrogenation zone by distillation.
It has been discovered that after distillation of the MCHM from
hydrogenation product from the second hydrogenation zone, the
distillation bottoms can separate into a lower layer comprising a
majority of the 1,4-cyclohexanedimethanol in the distillation bottoms and
an upper layer comprising a majority of the
4,4'-oxybis(methylene)bis(methylcyclohexane) (III) and other impurities
in the distillation bottoms. The term "majority," is intended to have its
commonly accepted meaning of "the greater part." For example, the phrase
"a majority of the 4,4'-oxybis(methylene)bis(methylcyclohexane) in the
distillation bottoms" is intended to mean greater than half of the total
amount of the 4,4'-oxybis(methylene)-bis(methylcyclohexane) that is
present in the distillation bottoms. The layers can be readily separated
and CHDM recovered and purified by a simple distillation of the lower
layer. The upper layer, containing the MCHM-diether and other impurities
can be discarded or used in other applications. Our invention, therefore,
provides a simplified method for the preparation and purification of the
CHDM. Hence, another embodiment of the invention is a process for the
preparation of 1,4-cyclohexanedimethanol, comprising: [0076] (i).
contacting bis(4-methylcyclohexyl)methyl) terephthalate with hydrogen in
a first hydrogenation zone in the presence of a catalyst effective for
hydrogenation of an aromatic ring to produce a liquid effluent comprising
bis(4-methylcyclohexyl)-methyl)cyclohexane-1,4-dicarboxylate; [0077]
(ii). contacting the effluent from the first hydrogenation zone with
hydrogen in the presence of an ester hydrogenation catalyst in a second
hydrogenation zone to produce a hydrogenation product comprising
1,4-cyclohexanedimethanol, 4,4'-oxybis(methylene)bis(methylcyclohexane),
and (4-methylcyclohexyl)methanol; [0078] (iii). distilling the
hydrogenation product from step (ii) to recover a distillate comprising a
majority of the (4-methylcyclohexyl)methanol in the hydrogenation product
and a distillation bottoms comprising a majority of the
1,4-cyclohexane-dimethanol, and
4,4'-oxybis(methylene)bis(methylcyclohexane)in the hydrogenation product;
[0079] (iv). allowing the distillation bottoms to form a lower layer
comprising a majority of the 1,4-cyclohexanedimethanol in the
distillation bottoms and a upper layer comprising a majority of the
4,4'-oxybis(methylene)bis(methylcyclohexane) in the distillation bottoms;
and [0080] (v). separating the upper and lower layers of step (iv) and
recovering the 1,4-cyclo-hexanedimethanol from the lower layer by
distillation. It should be understood that the above process comprises
the various embodiments of the esterification process, hydrogenation
steps, catalysts, temperature, pressure, reactor configurations, and
products as described hereinabove in any combination.

[0081] For example, the bis(4-methylcyclohexyl)methyl) terephthalate may
be produced by esterification of terephthalic acid with
(4-methylcyclohexyl)methanol and can be hydrogenated by contacting with
hydrogen at a temperature of about 150 to about 350° C. and a
pressure of about 50 to about 400 bar gauge in the presence of a catalyst
comprising palladium, platinum, nickel, ruthenium or combinations thereof
deposited on a catalyst support material. In another embodiment of our
process, the bis(4-methylcyclo-hexyl)methyl)terephthalate may be
contacted with hydrogen at a temperature of about 180 to about
250° C. and a pressure of about 50 to about 170 bar gauge, the
catalyst comprises palladium, ruthenium, or combinations thereof, and the
catalyst support material comprises alumina, silica-alumina, titania,
zirconia, chromium oxides, graphite, silicon carbide, or combinations
thereof. In still another embodiment, the catalyst in step (i) comprises
palladium on alumina.

[0082] The effluent from the first hydrogenation zone can be contacted
with hydrogen at a temperature of 180 to about 300° C. at a
pressure of about 40 to about 400 bar gauge in the presence of an ester
hydrogenation catalyst comprising at least one Group VIII metal, a
copper-containing catalyst, or a combination thereof. Some representative
examples of the ester hydrogenation catalyst include copper chromite,
copper oxide, Raney nickel, Raney cobalt, or combinations thereof. These
catalysts may be optionally promoted with zinc, barium, calcium,
manganese, magnesium, nickel, ruthenium, lanthanum, titanium, or a
combination thereof.

[0083] As noted above, after distillation of the MCHM from the
hydrogenation product of step (ii) of the process, the distillation
bottoms form an upper and lower layer wherein the lower layer comprises
most of the CHDM product that was present in the distillation bottoms and
the upper layer comprises the majority of the
4,4'-oxybis(methylene)bis-(methylcyclohexane) and other impurities in the
distillation bottoms. For example, the lower layer comprises at least 50
weight percent of 1,4-cyclohexanedimethanol, based on the total weight of
the lower layer. In another example, the upper layer comprises at least
70 weight percent of 4,4'-oxybis(methylene)bis(methylcyclohexane) based
on the total weight of the upper layer. The CHDM may be recovered from
the lower layer by distillation.

[0084] The MCHM that is recovered from the hydrogenation product in step
(iii) of the process can be passed to a process for the preparation of
bis(4-methylcyclohexyl)methyl) terephthalate by esterification of
terephthalic acid. Recycling the MCHM recovered in this manner utilizes
by-products that are produced in the overall CHDM process, avoids the
introduction of additional materials such as, for example, alcohols that
used for the preparation of terephthalate ester feedstocks, and
simplifies the purification of the feedstocks and the final product.
Another embodiment of our invention, therefore, is a process for the
preparation of 1,4-cyclohexanedimethanol, comprising: [0085] (i).
feeding an esterification reaction product comprising
bis(4-methylcyclohexyl)-methyl)terephthalate and
(4-methylcyclohexyl)methanol with hydrogen to a first hydrogenation zone
comprising a fixed bed of a palladium on alumina catalyst at a
temperature of about 180° C. to about 250° C. and a
pressure of about 50 to about 170 bar gauge to produce a liquid effluent
comprising bis(4-methylcyclohexyl)-methyl cyclohexane-1,4-dicarboxylate;
[0086] (ii). feeding the liquid effluent from step (i) with hydrogen to a
second hydrogenation zone comprising a fixed bed of a copper chromite
catalyst at a temperature of about 180 to about 300° C. and a
pressure of about 100 to about 400 bar gauge to produce a hydrogenation
product comprising 1,4-cyclohexanedimethanol,
(4-methylcyclohexyl)methanol, and
4,4'-oxybis(methylene)bis(methylcyclohexane); [0087] (iii). distilling
the hydrogenation product from step (ii) to recover a distillate
comprising a majority of the (4-methylcyclohexyl)methanol in the
hydrogenation product and a distillation bottoms comprising a majority of
the 1,4-cyclohexane-dimethanol and
4,4'-oxybis(methylene)bis(methylcyclohexane) in the hydrogenation
product; [0088] (iv). allowing the distillation bottoms to form a lower
layer comprising a majority of the 1,4-cyclohexanedimethanol in the
distillation bottoms and an upper layer comprising a majority of the
4,4'-oxybis(methylene)bis(methylcyclohexane) in the distillation bottoms;
[0089] (v). separating the upper and lower layers of step (iv) and
recovering the 1,4-cyclo-hexanedimethanol from the lower layer by
distillation; and [0090] (vi). passing the (4-methylcyclohexyl)methanol
from the distillate in step (iii) to an esterification process to produce
bis(4-methylcyclohexyl)methyl) terephthalate. It is intended that the
above process include the various embodiments of the esterification
process, hydrogenation steps, catalysts, temperature, pressure, reactor
configurations, and products as described hereinabove in any combination.

[0091] In one embodiment of the above process, for example, the lower
layer comprises at least 50 weight percent of 1,4-cyclohexanedimethanol,
based on the total weight of the lower layer. In another example, the
upper layer contains 5 weight percent or less of
1,4-cyclohexanedimethanol, based on the total weight of the upper layer.

[0092] As noted previously, the upper layer contains the major portion of
the MCHM-diether, i.e., 4,4'-oxybis(methylene)bis(methylcyclohexane)
(III), that was present in the distillation bottoms. For example, the
upper layer may comprise at least 70 weight percent of
4,4'-oxybis(methylene)bis(methylcyclohexane) based on the total weight of
the upper layer. In another example, the upper layer can comprise at
least 80 weight percent of 4,4'-oxybis(methylene)bis(methylcyclohexane)
based on the total weight of the upper layer.

[0093] The MCHM that is recovered from the hydrogenation product in step
(iii) of the process can be recycled by passing the recovered MCHM to a
process for the preparation of bis(4-methylcyclohexyl)methyl)
terephthalate by esterification of terephthalic acid. In one embodiment
of the process, the amount of MCHM recovered in step (iii) is sufficient
to prepare the entire esterification reaction product of step (i) that is
required for the downstream CHDM process.

[0094] The esterification, hydrogenation, and purification steps described
hereinabove can be combined to form an integrated process for the
preparation CHDM from terephthalic acid in which the only exogenous
feedstock is terephthalic acid. Yet another aspect of the instant
invention, therefore, is a process for the preparation of a
1,4-cyclo-hexanedimethanol from terephthalic acid, comprising [0095]
(i). contacting terephthalic acid and (4-methylcyclohexyl)methanol in a
mole ratio of alcohol to acid of at least 2:1, in a reaction zone at a
temperature of about 200° C. to about 300° C. under
superatmospheric pressure, while removing water from the reaction zone,
to form an esterification product mixture comprising
bis(4-methyl-cyclohexyl)methyl)terephthalate and unreacted
(4-methylcyclohexyl)methanol; [0096] (ii). contacting the esterification
product mixture with hydrogen in a first hydrogenation zone in the
presence of a catalyst effective for hydrogenation of an aromatic ring to
produce a liquid effluent comprising
bis(4-methylcyclohexyl)-methyl)cyclohexane-1,4-dicarboxylate; [0097]
(iii). contacting the effluent from the first hydrogenation zone with
hydrogen in the presence of an ester hydrogenation catalyst in a second
hydrogenation zone to produce a hydrogenation product comprising
1,4-cyclohexanedimethanol, 4,4'-oxybis(methylene)bis(methylcyclohexane),
and (4-methylcyclohexyl)methanol; [0098] (iv). distilling the
hydrogenation product from step (iii) to recover a distillate comprising
a majority of the (4-methylcyclohexyl)methanol in the hydrogenation
product and a distillation bottoms comprising a majority of the
1,4-cyclohexane-dimethanol and
4,4'-oxybis(methylene)bis(methylcyclohexane) in the hydrogenation
product; [0099] (v). allowing the distillation bottoms to form an lower
layer comprising a majority of the 1,4-cyclohexanedimethanol in the
distillation bottoms and a upper layer comprising a majority of the
4,4'-oxybis(methylene)bis(methylcyclohexane) in the distillation bottoms;
[0100] (vi). separating the upper and lower layers of step (v) and
recovering the 1,4-cyclo-hexanedimethanol from the lower layer by
distillation; and [0101] (vii). recycling at least a portion of the
(4-methylcyclohexyl)methanol from step (iv) to step (i). The above
process includes the various embodiments of the esterification process,
hydrogenation steps, catalysts, temperature, pressure, reactor
configurations, and products as described hereinabove in any combination.

[0102] In one embodiment, for example, the TPA and MCHM are contacted in a
reaction zone at a temperature of about 200 to about 300° C. at a
pressure of about 1.4 bar gauge to about 50 bar gauge. Other examples of
pressure and temperature that the esterification step may be operated at
are about 220 to about 280° C. at a pressure of about 1.4 to about
21 bar gauge, and about 240 to about 270° C. at about 1.4 to about
6.9 bar gauge. The molar ratio of alcohol to acid that can be used is
typically at least 2:1. Some additional examples of molar ratios of
alcohol to acid in the esterification step include about 2:1 to about
9:1; about 2:1 to about 8:1; about 2:1 to about 7:1; about 2:1 to about
5:1; about 2:1 to about 4:1; and about 2:1 to about 3:1.

[0103] The removal of the water may be accomplished by any conventional
means known to persons skilled in the art such as, for example,
distillation, membrane separation, the use of absorbents, or combinations
thereof. In one embodiment of the process of the invention, the water for
the esterification is removed from the reaction zone by distillation and
step (i) further comprises recovering (4-methylcyclohexyl)methanol from
the esterification product mixture by distillation and recycling to the
reaction zone of step (i). In one embodiment, for example, the water
and/or the MCHM may be removed by distillation of a water / MCHM
azeotrope, followed by separation of the water and MCHM layers. The water
may then be removed from the process and the MCHM returned or recycled to
the esterification reaction zone of step (i).

[0104] The esterification reaction may be carried in the presence or
absence of an exogenous esterification catalyst, i.e., a catalyst other
than terephthalic acid, that is added to the reaction mixture for the
purpose of increasing the rate of the esterification reaction. Any
esterification catalyst that is known in art may be used. For example,
the TPA and MCHM can be contacted in the presence of a catalyst
comprising compounds of titanium, magnesium, aluminum, boron, silicon,
tin, zirconium, zinc, antimony, manganese, calcium, vanadium, sulfuric
acid, p-toluene sulfonic acid, methane sulfonic acid, or phosphoric acid.
Although the esterification process may be carried out in the presence of
a catalyst, the reaction proceeds smoothly without added catalysts. Thus,
in one embodiment of the invention, the TPA and MCHM are contacted in the
absence of an exogenous catalyst. Conducting the esterification reaction
step in the absence of a catalyst avoids the need for additional
purification steps to remove catalyst residues which can poison the
hydrogenation catalysts or catalyze the formation of color bodies and
other undesirable by-products in the subsequent steps of the instant
process.

[0105] The hydrogenation product from the second hydrogenation zone
comprises, in addition to other products, MCHM that was present in the
esterification product mixture, released during the hydrogenation of the
bis(4-methylcyclohexyl)methyl) cyclohexane-1,4-dicarboxylate, and
additionally produced as a by-product. All or a portion of this MCHM can
be recovered, by distillation for example, and recycled to the
esterification step (i) of the process of the invention. In one
embodiment of the invention, all or a portion of the
(4-methylcyclohexyl)methanol that is contacted with the terephthalic acid
is recycled from the hydrogenation product of the second hydrogenation
zone. For example, the MCHM recovered from the hydrogenation product can
be combined with the MCHM recovered the esterification product mixture
and recycled back to the esterification reaction. In another embodiment,
all of the MCHM used in the esterification is recovered MCHM from the
hydrogenation product of the second hydrogenation zone.

[0106] The process of the present invention may be carried out in a batch,
semi-continuous or continuous mode. In one example, continuous operation
may involve continuously or intermittently feeding TPA and MCHM to and
continuously or intermittently removing alcohol, water and
product-containing reaction mixture from a pressure vessel maintained at
a predetermined temperature, pressure and liquid level; continuously
passing the esterification product mixture to the first hydrogenation
zone; continuously passing the effluent from the first hydrogenation zone
to the second hydrogenation zone; continuously distilling the MCHM from
the hydrogenation product of the second hydrogenation zone; continuously
allowing the distillation bottoms to separate into upper and lower
layers; continuously separating the layers and distilling CHDM from the
lower layer; and continuously recycling the MCHM recovered from the
hydrogenation product back to the esterification step. It will be
apparent to those skilled in the art that other reactor schemes may be
used with this invention. For example, the esterification and
hydrogenation reaction steps can be conducted in a plurality of reaction
zones, in series, in parallel, or it may be conducted batch wise or
continuously in a tubular plug flow reaction zone or series of such zones
with recycle of unconsumed feed substrate materials if required. For
example, the terephthalic acid and MCHM can be contacted in a fixed bed
or stirred reactor. As described hereinabove, the terephthalic acid also
may be added incrementally to the reaction zone. In another example, the
esterification reaction mixture may be fed to one or more secondary
reaction vessels wherein conversion of TPA and/or TPA half-ester to the
diester product is completed.

[0107] The esterification product mixture typically will comprise at least
50 weight percent of bis(4-methylcyclohexyl)methyl) terephthalate based
on the total weight of the esterification product mixture. Other examples
of weight percentages of bis(4-methyl-cyclohexyl)methyl)terephthalate in
the esterification product mixture are at least 60 weight percent, at
least 70 weight percent, at least 80 weight percent, and at least 90
weight percent.

[0108] Various embodiments of the first and second hydrogenation zone have
been described above. For example, the esterification product mixture in
step (ii) may be contacted with hydrogen at a temperature of about 150 to
about 350° C. and a pressure of about 50 to about 400 bar gauge in
the presence of a catalyst effective for hydrogenating an aromatic ring
comprising palladium, platinum, nickel, ruthenium or combinations thereof
deposited on a catalyst support material. In another example, the
esterification product mixture in step (ii) is contacted with hydrogen at
a temperature of about 180 to about 300° C. and a pressure of
about 50 to about 170 bar gauge, and the catalyst effective for
hydrogenating an aromatic ring comprises palladium, ruthenium, or
combinations thereof, and the catalyst support material comprises
alumina, silica-alumina, titania, zirconia, chromium oxides, graphite,
silicon carbide, or combinations thereof. In yet another example, the
catalyst effective for hydrogenating an aromatic ring comprises palladium
on alumina.

[0109] The effluent from the first hydrogenation zone, comprising
bis(4-methyl-cyclohexyl)methyl)cyclohexane-1,4-dicarboxylate (II), can be
contacted with hydrogen at a temperature of 180 to about 300° C.
at a pressure of about 40 to about 400 bar gauge in the presence of an
ester hydrogenation catalyst comprising at least one Group VIII metal, a
copper-containing catalyst, or a combination thereof. Some representative
examples of ester hydrogenation catalysts include copper chromite, copper
oxide, Raney nickel, Raney cobalt, or combinations thereof, and
optionally promoted with zinc, barium, calcium, manganese, magnesium,
nickel, ruthenium, or lanthanum.

[0110] Yet another embodiment of our novel CHDM process is a process for
the preparation of a 1,4-cyclohexanedimethanol from terephthalic acid,
comprising [0111] (i). contacting terephthalic acid and
(4-methylcyclohexyl)methanol in a mole ratio of alcohol to acid of about
2:1 to about 5:1, in a reaction zone at a temperature of about
220° C. to about 280° C. in the absence of a exogenous
catalyst under super atmospheric pressure, while distilling water from
the reaction zone, to form an esterification product mixture comprising
bis(4-methylcyclohexyl)methyl) terephthalate and unreacted
(4-methylcyclohexyl)methanol; [0112] (ii). recovering unreacted
(4-methylcyclohexyl)methanol from esterification product mixture by
distillation to form a purified esterification product mixture and
recycling the unreacted (4-methylcyclohexyl)methanol to the reaction zone
of step (i); [0113] (iii). contacting the purified esterification product
mixture with hydrogen in a first hydrogenation zone in the presence of a
palladium on alumina catalyst to produce a liquid effluent comprising
bis(4-methylcyclohexyl)methyl) cyclohexane-1,4-dicarboxylate; [0114]
(iv). contacting the effluent from the first hydrogenation zone with
hydrogen in the presence of a copper chromite catalyst in a second
hydrogenation zone to produce a hydrogenation product comprising
1,4-cyclohexanedimethanol, 4,4'-oxybis-(methylene)bis(methylcyclohexane),
and (4-methylcyclohexyl)methanol; [0115] (v). distilling the
hydrogenation product from step (iv) to recover a distillate comprising a
majority of the (4-methylcyclohexyl)methanol in the hydrogenation product
and a distillation bottoms comprising a majority of the
1,4-cyclohexane-dimethanol and
4,4'-oxybis(methylene)bis(methylcyclohexane) in the hydrogenation
product; [0116] (vi). allowing the distillation bottoms to form a lower
layer comprising a majority of the 1,4-cyclohexanedimethanol in the
distillation bottoms and an upper layer comprising a majority of the
4,4'-oxybis(methylene)bis(methylcyclohexane) in the distillation bottoms;
[0117] (vii). separating the upper and lower layers of step (vi) and
recovering the 1,4-cyclo-hexanedimethanol from the lower layer by
distillation; and [0118] (viii). recycling at least a portion of the
(4-methylcyclohexyl)methanol from step (v) to the reaction zone of step
(i). It is understood that the above process comprises the various
embodiments of the esterification process, hydrogenation steps,
catalysts, temperature, pressure, reactor configurations, and products as
described hereinabove in any combination.

[0119] In one embodiment, for example, the amount of MCHM in the
hydrogenation product of step (iv) is sufficient to satisfy the MCHM
required for the esterification reaction of step (i). In another
embodiment, all or a portion of the MCHM that is contacted with the
terephthalic acid is recycled from the hydrogenation product of the
second hydrogenation zone. For example, the MCHM recovered from the
hydrogenation product can be combined with the MCHM recovered the
esterification product mixture and recycled back to the esterification
reaction. In another embodiment, all of the MCHM used in the
esterification is recovered MCHM from the hydrogenation product of the
second hydrogenation zone. In yet another embodiment, the above process
may be operated entirely or in part as a continuous process.

[0120] Following distillation of the hydrogenation product from the second
hydrogenation zone, the distillation bottoms separates into an upper
layer comprising most of the MCHM-diether and impurities that were
present in the distillation bottoms and a lower layer comprising most of
the CHDM that was present in the distillation bottoms. For example, the
upper layer can contain 10 weight percent or less of
1,4-cyclohexanedimethanol, based on the total weight of the upper layer.
In another example, the upper layer can contain 5 weight percent or less
of 1,4-cyclohexanedimethanol, based on the total weight of the lower
layer. In another example, the upper layer can comprise at least 70
weight percent of 4,4'-oxybis(methylene)bis(methylcyclohexane) based on
the total weight of the upper layer. In still another example, the upper
layer can comprise at least 80 weight percent of
4,4'-oxybis(methylene)bis(methylcyclohexane) based on the total weight of
the upper layer.

[0121] The invention also includes the following embodiments that are set
forth in items 1-23 below:

[0122] 1. A process for the preparation of a 1,4-cyclohexanedimethanol
from terephthalic acid, comprising [0123] (i). contacting terephthalic
acid and (4-methylcyclohexyl)methanol in a mole ratio of alcohol to acid
of at least 2:1, in a reaction zone at a temperature of about 200°
C. to about 300° C. under superatmospheric pressure, while
removing water from the reaction zone, to form an esterification product
mixture comprising bis(4-methylcyclohexyl)methyl)terephthalate and
unreacted (4-methylcyclohexyl)-methanol; [0124] (ii). contacting the
esterification product mixture with hydrogen in a first hydrogenation
zone in the presence of a catalyst effective for hydrogenation of an
aromatic ring to produce a liquid effluent comprising
bis(4-methylcyclohexyl)-methyl)cyclohexane-1,4-dicarboxylate; [0125]
(iii). contacting the effluent from the first hydrogenation zone with
hydrogen in the presence of an ester hydrogenation catalyst in a second
hydrogenation zone to produce a hydrogenation product comprising
1,4-cyclohexanedimethanol, 4,4'-oxybis(methylene)bis(methylcyclohexane),
and (4-methylcyclohexyl)methanol; [0126] (iv). distilling the
hydrogenation product from step (iii) to recover a distillate comprising
a majority of the (4-methylcyclohexyl)methanol in the hydrogenation
product and a distillation bottoms comprising a majority of the
1,4-cyclo-hexanedimethanol and
4,4'-oxybis(methylene)bis(methylcyclohexane) in the hydrogenation
product; [0127] (v). allowing the distillation bottoms to form an lower
layer comprising a majority of the 1,4-cyclohexanedimethanol in the
distillation bottoms and a upper layer comprising a majority of the
4,4'-oxybis(methylene)bis(methylcyclohexane) in the distillation bottoms;
[0128] (vi). separating the upper and lower layers of step (v) and
recovering the 1,4-cyclo-hexanedimethanol from the lower layer by
distillation; and [0129] (vii) recycling at least a portion of the
(4-methylcyclohexyl)methanol to step (i).

[0130] 2. A process that includes the embodiments of item 1, wherein the
temperature in step (i) is about 220° C. to about 280° C.
and the pressure is about 1.4 bars gauge to about 6.9 bars gauge.

[0131] 3. A process that includes the embodiments of any one of items 1-2,
wherein the ratio of alcohol to acid in step (i) is about 2:1 to about
3:1.

[0132] 4. A process that includes the embodiments of any one of items 1-3,
wherein the water is removed from the reaction zone in step (i) by
distillation and wherein step (i) further comprises recovering
(4-methylcyclohexyl)methanol from the esterification product mixture by
distillation and recycling to the reaction zone of step (i).

[0133] 5. A process that includes the embodiments of any one of items 1-4,
wherein the terephthalic acid and (4-methylcyclohexyl)methanol are
contacted in the absence of an exogenous catalyst.

[0134] 6. A process that includes the embodiments of any one of items 1-5,
wherein all or a portion of the (4-methylcyclohexyl)methanol is contacted
with the terephthalic acid is recycled from process for the preparation
of CHDM by hydrogenation of bis(4-methyl-cyclohexyl)methyl)terephthalate.

[0135] 7. A process that includes the embodiments of any one of items 1-6,
wherein the process is a continuous process.

[0136] 8. A process that includes the embodiments of any one of items 1-7,
wherein the esterification product mixture comprises at least 70 weight
percent of bis(4-methylcyclo-hexyl)methyl)terephthalate.

[0137] 9. A process that includes the embodiments of any one of items 1-8,
which comprises contacting the terephthalic acid and
(4-methylcyclohexyl)methanol in a fixed bed or stirred reactor.

[0138] 10. A process that includes the embodiments of any one of items
1-9, wherein the terephthalic acid is added incrementally to the reaction
zone in step (i).

[0139] 11. A process that includes the embodiments of any one of items
1-10, wherein the esterification product mixture in step (ii) is
contacted with hydrogen at a temperature of about 150 to about
350° C. and a pressure of about 50 to about 400 bars gauge and the
catalyst effective for hydrogenating an aromatic ring comprises
palladium, platinum, nickel, ruthenium or combinations thereof deposited
on a catalyst support material.

[0140] 12. A process that includes the embodiments of any one of items
1-11, wherein the esterification product mixture in step (ii) is
contacted with hydrogen at a temperature of about 180 to about
300° C. and a pressure of about 50 to about 170 bars gauge, the
catalyst effective for hydrogenating an aromatic ring comprises
palladium, ruthenium, or combinations thereof, and the catalyst support
material comprises alumina, silica-alumina, titania, zirconia, chromium
oxides, graphite, silicon carbide, or combinations thereof.

[0141] 13. A process that includes the embodiments of any one of items
1-12, wherein the catalyst effective for hydrogenating an aromatic ring
comprises palladium on alumina.

[0142] 14. A process that includes the embodiments of any one of items
1-13, wherein the effluent from the first hydrogenation zone in step
(iii) is contacted with hydrogen at a temperature of 180 to about
300° C. at a pressure of about 40 to about 400 bars gauge and the
ester hydrogenation catalyst comprises at least one Group VIII metal, a
copper-containing catalyst, or a combination thereof.

[0144] 16. A process that includes the embodiments of any one of items
1-15, wherein in step (i), the terephthalic acid and
(4-methylcyclohexyl)methanol are contacted at a temperature of about
220° C. to about 280° C. in the absence of a exogenous
catalyst under super atmospheric pressure, while distilling water from
the reaction zone; in step (ii), the unreacted
(4-methylcyclohexyl)methanol is recovered from esterification product
mixture by distillation to form a purified esterification product mixture
and recycling the unreacted (4-methylcyclohexyl)methanol to the reaction
zone of step (i); in step (iii), the purified esterification product
mixture is contacted with hydrogen in a first hydrogenation zone in the
presence of a palladium on alumina catalyst to produce a liquid effluent
comprising bis(4-methylcyclohexyl)methyl) cyclohexane-1,4-dicarboxylate;
and, in step (iv), the effluent from the first hydrogenation zone is
contacted hydrogen in the presence of a copper chromite catalyst;

[0145] 17. A process that includes the embodiments of items 16, wherein
the amount of (4-methylcyclohexyl)methanol in the hydrogenation product
is sufficient to satisfy the (4-methylcyclohexyl)methanol required for
step (i).

[0146] 18. A process that includes the embodiments of any one of items
16-17, wherein all or a portion of the (4-methylcyclohexyl)methanol that
is contacted with the terephthalic acid is recycled from process for the
preparation of CHDM by hydrogenation of
bis(4-methylcyclohexyl)methyl)terephthalate.

[0147] 19. A process that includes the embodiments of any one of items
16-18, wherein the process is a continuous process.

[0148] 20. A process that includes the embodiments of any one of items
16-19, wherein the upper layer comprises 10 weight percent or less of
1,4-cyclohexanedimethanol, based on the total weight of the lower layer.

[0149] 21. A process that includes the embodiments of any one of items
16-20, wherein the upper layer comprises 5 weight percent or less of
1,4-cyclohexanedimethanol, based on the total weight of the lower layer.

[0150] 22. A process that includes the embodiments of any one of items
16-21, wherein the upper layer comprises at least 70 weight percent of
4,4'-oxybis(methylene)bis(methyl-cyclohexane) based on the total weight
of the upper layer.

[0151] 23. A process that includes the embodiments of any one of items
16-22, wherein the upper layer comprises at least 80 weight percent of
4,4'-oxybis(methylene)bis(methyl-cyclohexane) based on the total weight
of the upper layer.

EXAMPLES

[0152] The invention is further described and illustrated by the following
non-limiting examples.

Example 1

[0153] Esterification of terephthalic acid with
(4-methylcyclohexyl)-methanol--Terephthalic acid (10 moles) and 50 moles
of (4-methylcyclohexyl)methanol ("MCHM") were charged to an oil-jacketed
pilot scale batch reactor having a 2 gallon capacity, a pressure capacity
of 13.5 bar gauge (196 psig), and a vacuum capacity of ˜0.3 ton.
The reactor had a double helical stirrer that provided moderate mixing.
The unit was equipped with a side sample port allowing direct reaction
mixture sampling under pressure. A reflux condenser with separate hot oil
control was mounted directly to the unit head allowing partial
vapor/liquid separation. A water jacketed column was attached to the
reflux condenser to capture water and other liquid condensates.

[0154] The reactants were held at 5.0 bar gauge (73 psig), 260° C.,
and a column temperature of 150° C. with stirring for 5 hours and
20 minutes. The reaction appeared to be complete within 2 hours and 30
minutes. The column temperature increased to 156° C. and the water
of reaction was removed by distillation. An NMR spectrum showed that the
final conversion of terephthalic acid to bis(4-methylcyclohexyl)methyl)
terephthalate to be 94% based on the amount charged. In addition to
bis(4-methylcyclohexyl)methyl) terephthalate, gas chromatography/mass
spectroscopy ("GC/MS") showed no free TPA within detection limits, a
trace amount of the MCHM monoester of TPA, unreacted MCHM and trace
amounts of other impurities.

Example 2

[0155] Esterification of terephthalic acid with
(4-methylcyclohexyl)-methanol--Terephthalic acid (10 moles) and MCHM (50
moles) were charged to the same apparatus described in Example 1. The
reactants were held at 5.0 bar gauge (73 psig), 260° C., and a
column temperature of 150° C. with stirring for 3 hours. The
reactor temperature was increased to 270° C. and held for 1 hour
and 30 minutes. The water of reaction was removed by distillation. The
column set point was elevated to 180° C. during final hold time.
The reaction appeared to be complete within 2 hours and 30 minutes. At
the final conditions at 270° C., some additional MCHM condensate
was captured but little to no water of reaction was collected. Proton NMR
spectra showed final conversion of TPA to bis(4-methylcyclohexyl)methyl)
terephthalate of 96%. In addition to
bis(4-methylcyclohexyl)methyl)terephthalate, GC/MS showed a trace of TPA,
a trace amount of the MCHM monoester of TPA, unreacted MCHM and trace
amounts of other impurities.

Example 3

[0156] Esterification of terephthalic acid with
(4-methylcyclohexyl)-methanol--The esterification reaction of Example 2
was repeated with an additional 1 hour and 30 minutes of reaction time at
280° C. Proton NMR spectra showed the final conversion of TPA to
bis(4-methylcyclohexyl)methyl) terephthalate of 98%. The GC/MS analysis
was similar to that of Example 1.

Examples 4 and 5

[0157] Esterification of terephthalic acid with
(4-methylcyclohexyl)-methanol--The esterification reaction of Example 2
was repeated except that a TPA:MCHM molar ratio of 4:1 was used. The
reaction appeared to be complete after 31/2 hours. Proton NMR analysis
indicated a TPA conversion of 98 and 96%. GS/MS analysis showed similar
results to Example 2.

Examples 6 and 7

[0158] Esterification of terephthalic acid with
(4-methylcyclohexyl)-methanol--The esterification reaction of Example 2
was repeated except that a TPA:MCHM molar ratio of 3:1 was used. The
reaction appeared to be complete after 4 hours. Proton NMR analysis
indicated a TPA conversion of 92 and 97%. GS/MS analysis showed similar
results to Example 2, 4, and 5.

Examples 8 and 9

[0159] Esterification of terephthalic acid with
(4-methylcyclo-hexyl)methanol--The esterification reaction of Example 2
was repeated except that a TPA:MCHM molar ratio of 2:1 was used. The
reaction appeared to be complete after 4 hours. Proton NMR analysis
indicated a TPA conversion of 93 and 91%. GS/MS analysis showed similar
results to Example 2, 4, 5, 6, and 7.

Example 10 (Comparative)

[0160] Esterification of terephthalic acid with
(4-methyl-cyclohexyl)methanol--TPA (0.5 mole) and MCHM (2.0 moles) were
charged to a 500 mL round-bottomed flask (TPA:MCHM molar ratio of 4:1)
and stirred at 200° C. at atmospheric pressure for 48 hours.
Substantial quantities of undissolved TPA remained in the reaction vessel
and very little water was collected which indicated that the
esterification was incomplete. No analytical data was collected.

Example 11 (Comparative)

[0161] Esterification of terephthalic acid with
(4-methyl-cyclohexyl)methanol--The reaction of Example 10 was repeated
except that a TPA:MCHM molar ratio of 2:1 was used. The results were
similar to those obtained for Example 10.

Example 12

[0162] Esterification of terephthalic acid with
(4-methylcyclohexyl)-methanol--Seven experiments were carried out in
which TPA (2.5 moles) and MCHM (7.6 moles) were charged to an
electrically heated lab scale continuous stirred tank reactor having
about a 1 to 11/2 gallon capacity, a pressure capacity of 13.5 bar gauge
(196 psig) and equipped with an electrically traced distillation column
as well as a shell and tube hot oil jacketed condenser followed by a
shell and tube water jacketed condenser. The unit had a pitch blade
stirrer to provide moderate mixing. Water and other condensates were
captured in a water cooled vessel having a pressure rating at least equal
to and in line with the reactor. The reactants were stirred together at
4.8 bar gauge (70 psig) and 260° C. for 8 hours then at
270° C. for 1 hour, and finally at 280° C. for 1 hour. The
column temperature was 180° C. Analysis of the reaction product by
proton NMR showed that the TPA conversion for all seven experiments was
from 96 to 99%.

Example 13

[0163] Esterification of terephthalic acid with
(4-methylcyclohexyl)-methanol--Using the same apparatus as in Example 12,
four experiments were carried out in which TPA (2.5 moles) and MCHM (5.35
moles) were stirred together at pressures ranging from 2.4 to 5.2 bar
gauge (35-75 psig) for 7-8 hours. During the reaction the temperature was
increased from 140 to 295° C. TPA conversion was 91 to 98% by
proton NMR.

Example 14

[0164] Esterification of terephthalic acid with
(4-methylcyclohexyl)-methanol--Using the same apparatus as in Example 13,
two experiments were carried out in which TPA (2.5 moles) and MCHM (7.1
moles) were stirred together at 2.4 bar gauge (35 psig) for 8-9 hours.
During the reaction the temperature was increased from 255 to 275°
C. TPA conversion was 80 to 98% by NMR. The low conversion in one
experiment is believed to be from entrainment of TPA into the
distillation column and poor mixing.

Example 15

[0165] Batch hydrogenation of bis(4-methylcyclohexyl)methyl)terephthalate
to bis(4-methylcyclohexyl)methyl)cyclohexane-1,4-dicarboxylate--Bis(4-met-
hylcyclohexyl)methyl)terephthalate (abbreviated herein as "DXT") was
hydrogenated in a batch autoclave. DXT starting material was dissolved in
1,4-dimethycyclohexanedicarboxylate (abbreviated herein as "DMCD") at a
concentration of 20% by weight. This mixture (220 g) was loaded into a
batch autoclave with 10 g of Pd/Al2O3 catalyst and hydrogenated
for 1 hour at 124.1 bar gauge (1800 psig) and 200° C. Samples of
the feed material and final product material were collected and analyzed
by gas chromatography ("GC") with the area% results shown in Table 1. The
feed samples and reaction products and effluents were analyzed by
capillary gas chromatography using an Agilent Model 6890, or equivalent
gas chromatograph equipped with a thermal conductivity detector. Results
are given as area percentages. The GC samples (1 microliter) were
injected without dilution onto a 0.50 micron (30 m×0.25 mm) DB-WAX
column using a helium carrier gas. The GC column temperature was
maintained at 100° C. for 2 minutes, then programmed to
240° C. at 16° C. per minute. The final temperature of
240° C. was held for 20 minutes. The injection port used a 100:1
split ratio. In Table 1, the bis(4-methylcyclohexyl)methyl)
cyclohexane-1,4-dicarboxylate hydrogenation product is abbreviated as
"DXCD" and the by-product, (4-methylcyclohexyl)methyl
4-methylcyclohexanecarboxylate, is abbreviated as "MCHM ester." The
conversion of DXT to DXCD was 97%. The data also shows an increase in the
concentrations of MCHM and the MCHM ester.

[0166] The MCHM ester is thought to form as a hydrogenolysis product of
DXT and therefore represents a yield loss from the process. The
hydrogenolysis process also generates some MCHM.

Example 15

[0167] Batch hydrogenation of
bis(4-methylcyclohexyl)methyl)cyclohexane-1,4-dicarboxylate to
1,4-cyclohexanedimethanol ("CHDM")--DXCD (800 g of 83% DXCD with balance
MCHM and other impurities (1.7 moles of DXCD)) was hydrogenated at 4100
psi and 250° C. with 40 g of CuCr catalyst for 5 hours.
Approximately 95% of the starting DXCD was converted to CHDM during this
period as shown in the feed and product sample analyses in Table 2. In
Table 2, the MCHM monoester of TPA is labeled "Monoester." Analyses were
performed by gas chromatography and are shown as area percent.

Both CHDM and MCHM were coproduced during the reaction, and there were no
major additional byproducts observed. The CHDM cis/trans isomer ratio in
the final product was 0.35, which is near the equilibrium value.

Example 16

[0168] Continuous hydrogenation of DXT to DXCD--The DXT material was
continuously hydrogenated in a fixed bed reactor system at 124.1 bar
gauge (1800 psig) and 180-225° C. The experiments were carried out
in a continuous mode of operation utilizing a vertical trickle bed
reactor having a length of 72 inches and an inside diameter of 1 inch as
the reactor. The reactor temperature was measured with a series of 10
thermocouples inserted into the wall of the reactor. The reactor was
loaded with 830 mL (519 g) of Pd/alpha-Al2O3 catalyst
extrudates. The catalyst was supported by 20 mL of Penn State packing and
104 mL glass beads. An additional 400 mL of glass beads were placed on
top of the catalyst.

[0169] The feed reservoir was a jacketed, 4 L graduated vessel with a
bottom take-off valve. In this system, liquid feed material is added
through a high pressure syringe pump into a recycle stream and then
through a preheater to raise the feed temperature to the approximate
reactor temperature. The reservoir, pump head, and feed lines were steam
heated to prevent any feed material from freezing. Three zone heaters on
the reactor were used to establish an approximate isothermal temperature
profile during the experiment.

[0170] The DXT/recycle feed mixture was fed at the top of the reactor
vessel along with hydrogen and contacted with the catalyst. Crude product
was removed from the bottom of the reactor and fed to a level pot wherein
hydrogen was separated from the crude product. From the level pot, a
portion of the liquid is taken off as product with the remainder being
recycled to the top of the reactor. The liquid hold-up in the reactor
system was approximately 1 L. After the system reached the correct
process settings (temperature, pressure, feed rate, and recycle rate),
the system was held at equilibrium for the appropriate amount of time (3
full bed turnovers). Although the recycle rates were somewhat variable,
the typical recycle rate was estimated to be about 11-12 L/hr.

[0171] The GC area percent compositions of the DXT feed material and
hydrogenation product samples are shown in Table 3.

[0172] In these samples, most of the DXT was converted to the desired
product DXCD but also formed the MCHM ester and MCHM-diether as
impurities. The area percent concentration of the MCHM ester was nearly 8
times higher in the product than in the feed material. The formation of
the MCHM ester is believed to occur during the hydrogenolysis of DXT and,
thus, represents a yield loss to the process. Each mole of MCHM ester,
however, will hydrogenate to two moles of MCHM during the hydrogenation
of the ester groups. The MCHM-diether forms from the reaction of two MCHM
molecules, is relatively inert to reduction and, therefore, irreversibly
consumes MCHM.

Example 17

[0173] Continuous hydrogenation of DXT to DXCD--Using the sample reactor
system as described in Example 16, a second continuous hydrogenation of
DXT to DXCD was carried out using a DXT feed material that was prepared
in the absence of a catalyst in order to reduce the rate of diether
formation and thus limit the consumption of MCHM. In addition, the
hydrogenation was conducted at 137.9 bar gauge (2000 psig) using a low
acidity Pd/α-Al2O3 catalyst (750 mL, 662.8 g) and at
lower temperatures (200° C.). Analyses were performed by gas
chromatography and are shown as area percent in Table 4.

[0174] The ratio of MCHM diether to the desired product DXCD was
0.03-0.04. These values compare favorably to the ratio of 0.17 in Example
16 (shown in Table 3) and represent approximately a fourfold decrease.
Furthermore, the levels of MCHM diether and MCHM ester are nearly equal,
indicating that the process is neutral with respect to MCHM.

Example 18

[0175] Hydrogenolysis of DXCD to CHDM--The product of the first
hydrogenation shown in Table 3 was reacted further to produce CHDM. This
reaction was performed continuously in a trickle bed reactor at
225° C. and 344.7 bar gauge (5000 psig) using CuCr as a catalyst.
The GC area percent analyses of typical product samples are shown in
Table 5.

[0176] The hydrogenolysis of DXCD produces two moles of MCHM for every
mole of CHDM. The final product samples contain 12.9-13.1% CHDM dissolved
in MCHM. The product material contains lower concentrations of impurities
than the feed material, largely due to the reduction of the MCHM ester.
More than 90% of the MCHM ester is reduced during the hydrogenolysis
step, replacing some of the MCHM that was lost due to ether formation.
The ether itself is relatively inert and would have to be removed in
subsequent purification steps. Assuming that the area % concentrations
are equivalent to weight percent, the hydrogenolysis of DXCD was nearly
100% selective to the formation of DMCD and no significant byproducts
were observed during this step. The cis/trans isomer ratio of the CHDM
product was 0.42.

Example 19

[0177] Purification of CHDM from hydrogenation of DXCD--Crude final
product, comprising MCHM, CHDM, MCHM-diether, and other various
byproducts was isolated from a continuous hydrogenolysis run. The crude
product was analyzed by gas chromatography and shown below (trace
impurities excluded for simplicity) in Table 6. Three isomers of the
MCHM-diether can be seen in the gas chromatograph because of the
cis/trans isomers of the cyclohexane ring:

[0178] The above crude product was subjected to distillation to remove the
excess MCHM. This was accomplished on a vacuum still consisting of a
one-liter flask, magnetic stir bar, two 10'' Penn State packed columns
with feed port between the columns, a needle valve for feeding material,
feed tank, vapor take-off head, magnetic valve lifter, a condenser on the
vapor take-off head, a condenser for receiving material, fraction cutter,
receiver, three thermometers (base, feed, take-off vapor), and magnetic
stirrer. The distillation system was operated at about 10 torr and the
top take-off ratio was set at 35%. A table of the conditions, temperature
profile and feed rates is included below in Table 7 and analytical
results (GC, area %) are shown in Table 8.

[0179] As shown by analysis of the cuts from the still, very little CHDM
was lost to the recovered MCHM. After the distillation was complete, two
phases formed in the base, which formed a solid if allowed to cool to
room temperature. The phases were separated to give 804 g of a bottom
layer and 314.1 g of a top layer. The GC analyses (area %) of these
layers are shown in Table 9. The sum of the area percentages for each
layer was 98%.

[0180] The impurities labeled as "MW 268" and "MW 394" were identified by
GC-MS as (4-methylcyclohexyl)methyl
4-(hydroxymethyl)cyclohexane-l-carboxylate and
1-(4-methylcyclohexyl)methyl 4-octyl cyclohexane-1,4-dicarboxylate,
respectively. The composition of each layer is summarized in Table 10.

[0181] The bottom layer was distilled to remove MCHM diether using a
two-liter round bottom flask, stir bar, thermometer, 10'' Penn state
packed column, magnetic take-off head, condenser, fraction cutter, and
take-off receiver. The base was charged with the bottom layer from the
phase-separated mixture. Heat and vacuum was applied to the equipment and
the column was operated as summarized in Table 11:

[0182] After the ether removal step, the magnetic take-off head was
removed and replaced with a 3'' Vigreux column and heat tape applied to
take-off line to keep CHDM melted until collected. The distillation
profile is shown in Table 12 and an analysis of the distillation cuts is
provided in Table 13.